threads / patch / 55231

patch, 8 partsdiffcore-rename: enable filtering possible rename sources

Subject: [PATCH 1/8] diffcore-rename: enable filtering possible rename sources

## tl;dr

39 messages between Feb 28, 2021 and Mar 15, 2021. Diffs are folded; open one to read it.

replies: 38people: 2as markdown or json

Elijah Newren via GitGitGadget· Feb 28, 2021, 03:58 UTC · lore

[PATCH 0/8] Optimization batch 9: avoid detecting irrelevant renames

This series depends textually on ort-perf-batch-8, but semantically it's almost completely unrelated and can be reviewed without any familiarity with any of the previous patch series.

=== Basic Optimization idea ===

This series determines paths which meet special cases where detection of renames is irrelevant, where the irrelevance is due to the fact that the merge machinery will arrive at the same result regardless of whether a rename is detected for any of those paths. This series represents "Optimization #2" from my Git Merge 2020 talk[1], though this series has some improvements on the optimization relative to what I had at that time.

The basic idea here is that if side A of history:

 * only modifies/adds/deletes a few files
 * adds new files to few if any of the directories that side B deleted or
   renamed

then when we do rename detection on side B we can avoid even looking at most (and perhaps even all) paths that side B deleted. Since commits being rebased or cherry-picked tend to only modify a few files, this optimization tends to be particularly effective for rebases and cherry-picks.

Basing rename detection on what the other side of history did to a file means that extra information needs to be fed from merge-ort to diffcore-rename in order to take advantage of such an optimization.

=== Comparison to previous series ===

This series differs from my two previous optimizations[2][3] (focusing on basename-guided rename detection) in two important aspects:

 * there are no behavioral changes (there is no heuristic involved)

 * this optimization is merge specific (it does not help the diff/status/log
   family of commands, just merge/rebase/cherry-pick and such)

=== Results ===

For the testcases mentioned in commit 557ac0350d ("merge-ort: begin performance work; instrument with trace2_region_* calls", 2020-10-28), the changes in just this series improves the performance as follows:

                     Before Series           After Series
no-renames:       12.596 s ±  0.061 s     5.680 s ±  0.096 s
mega-renames:    130.465 s ±  0.259 s    13.812 s ±  0.162 s
just-one-mega:     3.958 s ±  0.010 s   506.0  ms ±  3.9  ms

However, interestingly, if we had ignored the basename-guided rename detection optimizations[2][3], then this optimization series would have improved the performance as follows:

               Before Basename Series   After Just This Series
no-renames:      13.815 s ±  0.062 s      5.728 s ±  0.104 s
mega-renames:  1799.937 s ±  0.493 s     18.213 s ±  0.139 s
just-one-mega    51.289 s ±  0.019 s    891.9  ms ±  7.0  ms

As a reminder, before any merge-ort/diffcore-rename performance work, the performance results we started with (as noted in the same commit message) were:

no-renames-am: 6.940 s ± 0.485 s no-renames: 18.912 s ± 0.174 s mega-renames: 5964.031 s ± 10.459 s just-one-mega: 149.583 s ± 0.751 s

=== Competition between optimizations ===

We now have three major rename-related optimizations:

 * exact rename detection
 * basename-guided rename detection[2][3]
 * skip-because-unnecessary (this series)

It is possible for all three to potentially apply for specific paths (they do for the majority of renamed paths in our testcases), but we cannot use more than one for any given path. It turns out that the priority we give each optimization is very important and can drastically affect performance. We get best results by prioritizing them as follows:

 1. exact rename detection
 2. skip-because-unnecessary
 3. basename-guided rename detection

The third-to-last patch of this series also discusses this ordering and another minor variant of the skip-because-unnecessary optimization that was tried (and resulted in less effective performance gains than reported here), as well as some of the preparatory work over the past few years that this series relies on in order to enable this optimization.

=== Near optimal? ===

You may remember that there was a row labelled "everything else" from the commit message of 557ac0350d that represented the maximum possible speed-up from accelerating rename detection alone; as stated in that commit, those rows represented how fast the code could be if we had somehow infinitely parallelized the inexact rename detection. However, if you compare those "maximum speedup" numbers to what we have above, you'll note that the infinitely parallelized inexact rename detection would have been slightly slower than the results we have now achieved. (The reason this is possible, despite the fact that we still spend time in rename detection after our optimizations, is because we implemented two optimizations outside of diffcore_rename() along the way.) However, this good news does also come with a downside -- it means that our remaining optimization potential is somewhat limited, and subsequent optimization series will have to fight for much smaller gains.

[1] https://github.com/newren/presentations/blob/pdfs/merge-performance/merge-performance-slides.pdf [2] https://lore.kernel.org/git/pull.843.git.1612651937.gitgitgadget@gmail.com/ [3] https://lore.kernel.org/git/pull.844.git.1613289544.gitgitgadget@gmail.com/

Elijah Newren (8):
  diffcore-rename: enable filtering possible rename sources
  merge-ort: precompute subset of sources for which we need rename
    detection
  merge-ort: add data structures for an alternate tree traversal
  merge-ort: introduce wrappers for alternate tree traversal
  merge-ort: precompute whether directory rename detection is needed
  merge-ort: use relevant_sources to filter possible rename sources
  merge-ort: skip rename detection entirely if possible
  diffcore-rename: avoid doing basename comparisons for irrelevant
    sources

 diffcore-rename.c |  63 ++++++++++---
 diffcore.h        |   1 +
 merge-ort.c       | 236 +++++++++++++++++++++++++++++++++++++++++++++-
 3 files changed, 285 insertions(+), 15 deletions(-)

base-commit: 4be565c472088d4144063b736308bf2a57331f45
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-845%2Fnewren%2Fort-perf-batch-9-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-845/newren/ort-perf-batch-9-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/845

-- 
gitgitgadget

Elijah Newren via GitGitGadget· Feb 28, 2021, 03:58 UTC · re: Elijah Newren via GitGitGadget · lore

From: Elijah Newren <newren@gmail.com>

Add the ability to diffcore_rename_extended() to allow external callers to declare that they only need renames detected for a subset of source files, and use that information to skip detecting renames for them.

There are two important pieces to this optimization that may not be obvious at first glance:

  * We do not require callers to just filter the filepairs out
    to remove the non-relevant sources, because exact rename detection
    is fast and when it finds a match it can remove both a source and a
    destination whereas the relevant_sources filter can only remove a
    source.

  * We need to filter out the source pairs in a preliminary pass instead
    of adding a
       strset_contains(relevant_sources, one->path)
    check within the nested matrix loop.  The reason for that is if we
    have 30k renames, doing 30k * 30k = 900M strset_contains() calls
    becomes extraordinarily expensive and defeats the performance gains
    from this change; we only want to do 30k such calls instead.

If callers pass NULL for relevant_sources, that is special cases to treat all sources as relevant. Since all callers currently pass NULL, this optimization does not yet have any effect. Subsequent commits will have merge-ort compute a set of relevant_sources to restrict which sources we detect renames for, and have merge-ort pass that set of relevant_sources to diffcore_rename_extended().

Signed-off-by: Elijah Newren <newren@gmail.com>
---
 diffcore-rename.c | 26 +++++++++++++++++++-------
 diffcore.h        |  1 +
 merge-ort.c       |  1 +
 3 files changed, 21 insertions(+), 7 deletions(-)

Show changes to 3 files +21 −7

diffcore-rename.c, diffcore.h, merge-ort.c

diff --git a/diffcore-rename.c b/diffcore-rename.c
index 1fe902ed2af0..7f6115fd9018 100644
--- a/diffcore-rename.c
+++ b/diffcore-rename.c
@@ -991,11 +991,12 @@ static int find_renames(struct diff_score *mx,
 	return count;
 }
 
-static void remove_unneeded_paths_from_src(int detecting_copies)
+static void remove_unneeded_paths_from_src(int detecting_copies,
+					   struct strset *interesting)
 {
 	int i, new_num_src;
 
-	if (detecting_copies)
+	if (detecting_copies && !interesting)
 		return; /* nothing to remove */
 	if (break_idx)
 		return; /* culling incompatible with break detection */
@@ -1022,12 +1023,18 @@ static void remove_unneeded_paths_from_src(int detecting_copies)
 	 *      from rename_src here.
 	 */
 	for (i = 0, new_num_src = 0; i < rename_src_nr; i++) {
+		struct diff_filespec *one = rename_src[i].p->one;
+
 		/*
 		 * renames are stored in rename_dst, so if a rename has
 		 * already been detected using this source, we can just
 		 * remove the source knowing rename_dst has its info.
 		 */
-		if (rename_src[i].p->one->rename_used)
+		if (!detecting_copies && one->rename_used)
+			continue;
+
+		/* If we don't care about the source path, skip it */
+		if (interesting && !strset_contains(interesting, one->path))
 			continue;
 
 		if (new_num_src < i)
@@ -1040,6 +1047,7 @@ static void remove_unneeded_paths_from_src(int detecting_copies)
 }
 
 void diffcore_rename_extended(struct diff_options *options,
+			      struct strset *relevant_sources,
 			      struct strset *dirs_removed,
 			      struct strmap *dir_rename_count)
 {
@@ -1060,6 +1068,8 @@ void diffcore_rename_extended(struct diff_options *options,
 	want_copies = (detect_rename == DIFF_DETECT_COPY);
 	if (dirs_removed && (break_idx || want_copies))
 		BUG("dirs_removed incompatible with break/copy detection");
+	if (break_idx && relevant_sources)
+		BUG("break detection incompatible with source specification");
 	if (!minimum_score)
 		minimum_score = DEFAULT_RENAME_SCORE;
 
@@ -1127,9 +1137,10 @@ void diffcore_rename_extended(struct diff_options *options,
 		/*
 		 * Cull sources:
 		 *   - remove ones corresponding to exact renames
+		 *   - remove ones not found in relevant_sources
 		 */
 		trace2_region_enter("diff", "cull after exact", options->repo);
-		remove_unneeded_paths_from_src(want_copies);
+		remove_unneeded_paths_from_src(want_copies, relevant_sources);
 		trace2_region_leave("diff", "cull after exact", options->repo);
 	} else {
 		/* Determine minimum score to match basenames */
@@ -1148,7 +1159,7 @@ void diffcore_rename_extended(struct diff_options *options,
 		 *   - remove ones involved in renames (found via exact match)
 		 */
 		trace2_region_enter("diff", "cull after exact", options->repo);
-		remove_unneeded_paths_from_src(want_copies);
+		remove_unneeded_paths_from_src(want_copies, NULL);
 		trace2_region_leave("diff", "cull after exact", options->repo);
 
 		/* Preparation for basename-driven matching. */
@@ -1167,9 +1178,10 @@ void diffcore_rename_extended(struct diff_options *options,
 		/*
 		 * Cull sources, again:
 		 *   - remove ones involved in renames (found via basenames)
+		 *   - remove ones not found in relevant_sources
 		 */
 		trace2_region_enter("diff", "cull basename", options->repo);
-		remove_unneeded_paths_from_src(want_copies);
+		remove_unneeded_paths_from_src(want_copies, relevant_sources);
 		trace2_region_leave("diff", "cull basename", options->repo);
 	}
 
@@ -1342,5 +1354,5 @@ void diffcore_rename_extended(struct diff_options *options,
 
 void diffcore_rename(struct diff_options *options)
 {
-	diffcore_rename_extended(options, NULL, NULL);
+	diffcore_rename_extended(options, NULL, NULL, NULL);
 }
diff --git a/diffcore.h b/diffcore.h
index c6ba64abd198..737c93a6cc79 100644
--- a/diffcore.h
+++ b/diffcore.h
@@ -166,6 +166,7 @@ void partial_clear_dir_rename_count(struct strmap *dir_rename_count);
 void diffcore_break(struct repository *, int);
 void diffcore_rename(struct diff_options *);
 void diffcore_rename_extended(struct diff_options *options,
+			      struct strset *relevant_sources,
 			      struct strset *dirs_removed,
 			      struct strmap *dir_rename_count);
 void diffcore_merge_broken(void);
diff --git a/merge-ort.c b/merge-ort.c
index 467404cc0a35..aba0b9fa54c3 100644
--- a/merge-ort.c
+++ b/merge-ort.c
@@ -2029,6 +2029,7 @@ static void detect_regular_renames(struct merge_options *opt,
 	diff_queued_diff = renames->pairs[side_index];
 	trace2_region_enter("diff", "diffcore_rename", opt->repo);
 	diffcore_rename_extended(&diff_opts,
+				 NULL,
 				 &renames->dirs_removed[side_index],
 				 &renames->dir_rename_count[side_index]);
 	trace2_region_leave("diff", "diffcore_rename", opt->repo);

-- 
gitgitgadget

Elijah Newren via GitGitGadget· Feb 28, 2021, 03:58 UTC · re: Elijah Newren via GitGitGadget · lore

[PATCH 3/8] merge-ort: add data structures for an alternate tree traversal

From: Elijah Newren <newren@gmail.com>

In order to determine whether directory rename detection is needed, we as a pre-requisite need a way to traverse through all the files in a given tree before visiting any directories within that tree. traverse_trees() only iterates through the entries in the order they appear, so add some data structures that will store all the entries as we iterate through them in traverse_trees(), which will allow us to re-traverse them in our desired order.

Signed-off-by: Elijah Newren <newren@gmail.com>
---
 merge-ort.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

Show changes to merge-ort.c +26 −0

diff --git a/merge-ort.c b/merge-ort.c
index 83aa4c08121f..d49cfa8b030b 100644
--- a/merge-ort.c
+++ b/merge-ort.c
@@ -51,6 +51,12 @@ enum merge_side {
 	MERGE_SIDE2 = 2
 };
 
+struct traversal_callback_data {
+	unsigned long mask;
+	unsigned long dirmask;
+	struct name_entry names[3];
+};
+
 struct rename_info {
 	/*
 	 * All variables that are arrays of size 3 correspond to data tracked
@@ -102,6 +108,22 @@ struct rename_info {
 	 */
 	struct strset relevant_sources[3];
 
+	/*
+	 * callback_data_*: supporting data structures for alternate traversal
+	 *
+	 * We sometimes need to be able to traverse through all the files
+	 * in a given tree before all immediate subdirectories within that
+	 * tree.  Since traverse_trees() doesn't do that naturally, we have
+	 * a traverse_trees_wrapper() that stores any immediate
+	 * subdirectories while traversing files, then traverses the
+	 * immediate subdirectories later.  These callback_data* variables
+	 * store the information for the subdirectories so that we can do
+	 * that traversal order.
+	 */
+	struct traversal_callback_data *callback_data;
+	int callback_data_nr, callback_data_alloc;
+	char *callback_data_traverse_path;
+
 	/*
 	 * needed_limit: value needed for inexact rename detection to run
 	 *
@@ -396,6 +418,10 @@ static void clear_or_reinit_internal_opts(struct merge_options_internal *opti,
 		}
 		strmap_clear(&opti->output, 0);
 	}
+
+	/* Clean out callback_data as well. */
+	FREE_AND_NULL(renames->callback_data);
+	renames->callback_data_nr = renames->callback_data_alloc = 0;
 }
 
 static int err(struct merge_options *opt, const char *err, ...)

-- 
gitgitgadget

Elijah Newren via GitGitGadget· Feb 28, 2021, 03:58 UTC · re: Elijah Newren via GitGitGadget · lore

[PATCH 2/8] merge-ort: precompute subset of sources for which we need rename detection

From: Elijah Newren <newren@gmail.com>

rename detection works by trying to pair all file deletions (or "sources") with all file additions (or "destinations"), checking similarity, and then marking the sufficiently similar ones as renames. This can be expensive if there are many sources and destinations on a given side of history as it results in an N x M comparison matrix. However, there are many cases where we can compute in advance that detecting renames for some of the sources provides no useful information and thus that we can exclude those sources from the matrix.

To see why, first note that the merge machinery uses detected renames in two ways:

   * directory rename detection: when one side of history renames a
       directory, and the other side of history adds new files to that
       directory, we want to be able to warn the user about the need to
       chose whether those new files stay in the old directory or move
       to the new one.

   * three-way content merging: in order to do three-way content merging
       of files, we need three different file versions.  If one side of
       history renamed a file, then some of the content for the file is
       found under a different path than in the merge base or on the
       other side of history.

This commit concentrates just on the three-way content merging; it will punt and mark all sources as needed for directory rename detection, and leave it to future commits to narrow that down more.

The point of three-way content merging is to reconcile changes made on *both* sides of history. What if the file wasn't modified on both sides? There are two possibilities:

   * If it wasn't modified on the renamed side:
       -> then we get to do exact rename detection, which is cheap.

   * If it wasn't modified on the unrenamed side:
       -> then detection of a rename for that source file is irrelevant

That latter claim might be surprising at first, so let's walk through a case to show why rename detection for that source file is irrelevant. Let's use two filenames, old.c & new.c, with the following abbreviated object ids (and where the value '000000' is used to denote that the file is missing in that commit):

                 old.c     new.c
   MERGE_BASE:   01d01d    000000
   MERGE_SIDE1:  01d01d    000000
   MERGE_SIDE2:  000000    5e1ec7

If the rename *isn't* detected:
   then old.c looks like it was unmodified on one side and deleted on
   the other and should thus be removed.  new.c looks like a new file we
   should keep as-is.

If the rename *is* detected:
   then a three-way content merge is done.  Since the version of the
   file in MERGE_BASE and MERGE_SIDE1 are identical, the three-way merge
   will produce exactly the version of the file whose abbreviated
   object id is 5e1ec7.  It will record that file at the path new.c,
   while removing old.c from the directory.

Note that these two results are identical -- a single file named 'new.c' with object id 5e1ec7. In other words, it doesn't matter if the rename is detected in the case where the file is unmodified on the unrenamed side.

Use this information to compute whether we need rename detection for each source created in add_pair().

It's probably worth noting that there used to be a few other edge or corner cases besides three-way content merges and directory rename detection where lack of rename detection could have affected the result, but those cases actually highlighted where conflict resolution methods were not consistent with each other. Fixing those inconsistencies were thus critically important to enabling this optimization. That work involved the following:

 * bringing consistency to add/add, rename/add, and rename/rename
    conflict types, as done back in the topic merged at commit
    ac193e0e0a ("Merge branch 'en/merge-path-collision'", 2019-01-04),
    and further extended in commits 2a7c16c980 ("t6422, t6426: be more
    flexible for add/add conflicts involving renames", 2020-08-10) and
    e8eb99d4a6 ("t642[23]: be more flexible for add/add conflicts
    involving pair renames", 2020-08-10)

  * making rename/delete more consistent with modify/delete
    as done in commits 1f3c9ba707 ("t6425: be more flexible with
    rename/delete conflict messages", 2020-08-10) and 727c75b23f
    ("t6404, t6423: expect improved rename/delete handling in ort
    backend", 2020-10-26)

Since the set of relevant_sources we compute has not yet been narrowed down for directory rename detection, we do not pass it to diffcore_rename_extended() yet. That will be done after subsequent commits narrow down the list of relevant_sources needed for directory rename detection reasons.

Signed-off-by: Elijah Newren <newren@gmail.com>
---
 merge-ort.c | 35 ++++++++++++++++++++++++++++++++---
 1 file changed, 32 insertions(+), 3 deletions(-)

Show changes to merge-ort.c +32 −3

diff --git a/merge-ort.c b/merge-ort.c
index aba0b9fa54c3..83aa4c08121f 100644
--- a/merge-ort.c
+++ b/merge-ort.c
@@ -88,6 +88,20 @@ struct rename_info {
 	 */
 	struct strmap dir_renames[3];
 
+	/*
+	 * relevant_sources: deleted paths for which we need rename detection
+	 *
+	 * relevant_sources is a set of deleted paths on each side of
+	 * history for which we need rename detection.  If a path is deleted
+	 * on one side of history, we need to detect if it is part of a
+	 * rename if either
+	 *    * we need to detect renames for an ancestor directory
+	 *    * the file is modified/deleted on the other side of history
+	 * If neither of those are true, we can skip rename detection for
+	 * that path.
+	 */
+	struct strset relevant_sources[3];
+
 	/*
 	 * needed_limit: value needed for inexact rename detection to run
 	 *
@@ -358,6 +372,8 @@ static void clear_or_reinit_internal_opts(struct merge_options_internal *opti,
 			strmap_clear(&renames->dir_rename_count[i], 1);
 
 		strmap_func(&renames->dir_renames[i], 0);
+
+		strset_func(&renames->relevant_sources[i]);
 	}
 
 	if (!reinitialize) {
@@ -533,12 +549,21 @@ static void add_pair(struct merge_options *opt,
 		     struct name_entry *names,
 		     const char *pathname,
 		     unsigned side,
-		     unsigned is_add /* if false, is_delete */)
+		     unsigned is_add /* if false, is_delete */,
+		     unsigned match_mask)
 {
 	struct diff_filespec *one, *two;
 	struct rename_info *renames = &opt->priv->renames;
 	int names_idx = is_add ? side : 0;
 
+	if (!is_add) {
+		unsigned content_relevant = (match_mask == 0);
+		unsigned location_relevant = 1; /* FIXME: compute this */
+
+		if (content_relevant || location_relevant)
+			strset_add(&renames->relevant_sources[side], pathname);
+	}
+
 	one = alloc_filespec(pathname);
 	two = alloc_filespec(pathname);
 	fill_filespec(is_add ? two : one,
@@ -575,11 +600,13 @@ static void collect_rename_info(struct merge_options *opt,
 
 		/* Check for deletion on side */
 		if ((filemask & 1) && !(filemask & side_mask))
-			add_pair(opt, names, fullname, side, 0 /* delete */);
+			add_pair(opt, names, fullname, side, 0 /* delete */,
+				 match_mask & filemask);
 
 		/* Check for addition on side */
 		if (!(filemask & 1) && (filemask & side_mask))
-			add_pair(opt, names, fullname, side, 1 /* add */);
+			add_pair(opt, names, fullname, side, 1 /* add */,
+				 match_mask & filemask);
 	}
 }
 
@@ -3228,6 +3255,8 @@ static void merge_start(struct merge_options *opt, struct merge_result *result)
 					 NULL, 1);
 		strmap_init_with_options(&renames->dir_renames[i],
 					 NULL, 0);
+		strset_init_with_options(&renames->relevant_sources[i],
+					 NULL, 0);
 	}
 
 	/*

-- 
gitgitgadget

Elijah Newren via GitGitGadget· Feb 28, 2021, 03:58 UTC · re: Elijah Newren via GitGitGadget · lore

[PATCH 4/8] merge-ort: introduce wrappers for alternate tree traversal

From: Elijah Newren <newren@gmail.com>

Add traverse_trees_wrapper() and traverse_trees_wrapper_callback() functions. The former runs traverse_trees() with info->fn set to traverse_trees_wrapper_callback, in order to simply save all the entries without processing or recursing into any of them. This step allows extra computation to be done (e.g. checking some condition across all files) that can be used later. Then, after that is completed, it iterates over all the saved entries and calls the original info->fn callback with the saved data.

Currently, this does nothing more than marginally slowing down the tree traversal since we do not take advantage of the opportunity to compute anything special in traverse_trees_wrapper_callback(), and thus the real callback will be called identically as it would have been without this extra wrapper. However, a subsequent commit will add some special computation of some values that the real callback will be able to use.

Signed-off-by: Elijah Newren <newren@gmail.com>
---
 merge-ort.c | 72 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 72 insertions(+)

Show changes to merge-ort.c +72 −0

diff --git a/merge-ort.c b/merge-ort.c
index d49cfa8b030b..bd2b93a31141 100644
--- a/merge-ort.c
+++ b/merge-ort.c
@@ -512,6 +512,78 @@ static char *unique_path(struct strmap *existing_paths,
 
 /*** Function Grouping: functions related to collect_merge_info() ***/
 
+static int traverse_trees_wrapper_callback(int n,
+					   unsigned long mask,
+					   unsigned long dirmask,
+					   struct name_entry *names,
+					   struct traverse_info *info)
+{
+	struct merge_options *opt = info->data;
+	struct rename_info *renames = &opt->priv->renames;
+
+	assert(n==3);
+
+	if (!renames->callback_data_traverse_path)
+		renames->callback_data_traverse_path = xstrdup(info->traverse_path);
+
+	ALLOC_GROW(renames->callback_data, renames->callback_data_nr + 1,
+		   renames->callback_data_alloc);
+	renames->callback_data[renames->callback_data_nr].mask = mask;
+	renames->callback_data[renames->callback_data_nr].dirmask = dirmask;
+	COPY_ARRAY(renames->callback_data[renames->callback_data_nr].names,
+		   names, 3);
+	renames->callback_data_nr++;
+
+	return mask;
+}
+
+/*
+ * Much like traverse_trees(), BUT:
+ *   - read all the tree entries FIRST, saving them
+ *   - note that the above step provides an opportunity to compute necessary
+ *     additional details before the "real" traversal
+ *   - loop through the saved entries and call the original callback on them
+ */
+MAYBE_UNUSED
+static int traverse_trees_wrapper(struct index_state *istate,
+				  int n,
+				  struct tree_desc *t,
+				  struct traverse_info *info)
+{
+	int ret, i, old_offset;
+	traverse_callback_t old_fn;
+	char *old_callback_data_traverse_path;
+	struct merge_options *opt = info->data;
+	struct rename_info *renames = &opt->priv->renames;
+
+	old_callback_data_traverse_path = renames->callback_data_traverse_path;
+	old_fn = info->fn;
+	old_offset = renames->callback_data_nr;
+
+	renames->callback_data_traverse_path = NULL;
+	info->fn = traverse_trees_wrapper_callback;
+	ret = traverse_trees(istate, n, t, info);
+	if (ret < 0)
+		return ret;
+
+	info->traverse_path = renames->callback_data_traverse_path;
+	info->fn = old_fn;
+	for (i = old_offset; i < renames->callback_data_nr; ++i) {
+		info->fn(n,
+			 renames->callback_data[i].mask,
+			 renames->callback_data[i].dirmask,
+			 renames->callback_data[i].names,
+			 info);
+
+	}
+
+	renames->callback_data_nr = old_offset;
+	free(renames->callback_data_traverse_path);
+	renames->callback_data_traverse_path = old_callback_data_traverse_path;
+	info->traverse_path = NULL;
+	return 0;
+}
+
 static void setup_path_info(struct merge_options *opt,
 			    struct string_list_item *result,
 			    const char *current_dir_name,

-- 
gitgitgadget

Elijah Newren via GitGitGadget· Feb 28, 2021, 03:58 UTC · re: Elijah Newren via GitGitGadget · lore

[PATCH 5/8] merge-ort: precompute whether directory rename detection is needed

From: Elijah Newren <newren@gmail.com>

The point of directory rename detection is that if one side of history renames a directory, and the other side adds new files under the old directory, then the merge can move those new files into the new directory. This leads to the following important observation:

  * If the other side does not add any new files under the old
    directory, we do not need to detect any renames for that directory.

Similarly, directory rename detection had an important requirement:

  * If a directory still exists on one side of history, it has not been
    renamed on that side of history.  (See section 4 of t6423 or
    Documentation/technical/directory-rename-detection.txt for more
    details).

Using these two bits of information, we note that directory rename
detection is only needed in cases where (1) directories exist in the
merge base and on one side of history (i.e. dirmask == 3 or dirmask ==
5), and (2) where there is some new file added to that directory on the
side where it still exists (thus where the file has filemask == 2 or
filemask == 4, respectively).  This has to be done in two steps, because
we have the dirmask when we are first considering the directory, and
won't get the filemasks for the files within it until we recurse into
that directory.  So, we save
  dir_rename_mask = dirmask - 1
when we hit a directory that is missing on one side, and then later look
for cases of
  filemask == dir_rename_mask

One final note is that as soon as we hit a directory that needs directory rename detection, we will need to detect renames in all subdirectories of that directory as well due to the "majority rules" decision when files are renamed into different directory hierarchies. We arbitrarily use the special value of 0x07 to record when we've hit such a directory.

The combination of all the above mean that we introduce a variable
named dir_rename_mask (couldn't think of a better name) which has one
of the following values as we traverse into a directory:
   * 0x00: directory rename detection not needed
   * 0x02 or 0x04: directory rename detection only needed if files added
   * 0x07: directory rename detection definitely needed

We then pass this value through to add_pairs() so that it can mark location_relevant as true only when dir_rename_mask is 0x07.

Signed-off-by: Elijah Newren <newren@gmail.com>
---
 merge-ort.c | 67 ++++++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 61 insertions(+), 6 deletions(-)

Show changes to merge-ort.c +61 −6

diff --git a/merge-ort.c b/merge-ort.c
index bd2b93a31141..27acaa7380be 100644
--- a/merge-ort.c
+++ b/merge-ort.c
@@ -108,6 +108,14 @@ struct rename_info {
 	 */
 	struct strset relevant_sources[3];
 
+	/*
+	 * dir_rename_mask:
+	 *   0: optimization removing unmodified potential rename source okay
+	 *   2 or 4: optimization okay, but must check for files added to dir
+	 *   7: optimization forbidden; need rename source in case of dir rename
+	 */
+	unsigned dir_rename_mask:3;
+
 	/*
 	 * callback_data_*: supporting data structures for alternate traversal
 	 *
@@ -419,6 +427,8 @@ static void clear_or_reinit_internal_opts(struct merge_options_internal *opti,
 		strmap_clear(&opti->output, 0);
 	}
 
+	renames->dir_rename_mask = 0;
+
 	/* Clean out callback_data as well. */
 	FREE_AND_NULL(renames->callback_data);
 	renames->callback_data_nr = renames->callback_data_alloc = 0;
@@ -520,12 +530,16 @@ static int traverse_trees_wrapper_callback(int n,
 {
 	struct merge_options *opt = info->data;
 	struct rename_info *renames = &opt->priv->renames;
+	unsigned filemask = mask & ~dirmask;
 
 	assert(n==3);
 
 	if (!renames->callback_data_traverse_path)
 		renames->callback_data_traverse_path = xstrdup(info->traverse_path);
 
+	if (filemask && filemask == renames->dir_rename_mask)
+		renames->dir_rename_mask = 0x07;
+
 	ALLOC_GROW(renames->callback_data, renames->callback_data_nr + 1,
 		   renames->callback_data_alloc);
 	renames->callback_data[renames->callback_data_nr].mask = mask;
@@ -544,7 +558,6 @@ static int traverse_trees_wrapper_callback(int n,
  *     additional details before the "real" traversal
  *   - loop through the saved entries and call the original callback on them
  */
-MAYBE_UNUSED
 static int traverse_trees_wrapper(struct index_state *istate,
 				  int n,
 				  struct tree_desc *t,
@@ -556,6 +569,8 @@ static int traverse_trees_wrapper(struct index_state *istate,
 	struct merge_options *opt = info->data;
 	struct rename_info *renames = &opt->priv->renames;
 
+	assert(renames->dir_rename_mask == 2 || renames->dir_rename_mask == 4);
+
 	old_callback_data_traverse_path = renames->callback_data_traverse_path;
 	old_fn = info->fn;
 	old_offset = renames->callback_data_nr;
@@ -648,7 +663,8 @@ static void add_pair(struct merge_options *opt,
 		     const char *pathname,
 		     unsigned side,
 		     unsigned is_add /* if false, is_delete */,
-		     unsigned match_mask)
+		     unsigned match_mask,
+		     unsigned dir_rename_mask)
 {
 	struct diff_filespec *one, *two;
 	struct rename_info *renames = &opt->priv->renames;
@@ -656,7 +672,7 @@ static void add_pair(struct merge_options *opt,
 
 	if (!is_add) {
 		unsigned content_relevant = (match_mask == 0);
-		unsigned location_relevant = 1; /* FIXME: compute this */
+		unsigned location_relevant = (dir_rename_mask == 0x07);
 
 		if (content_relevant || location_relevant)
 			strset_add(&renames->relevant_sources[side], pathname);
@@ -680,6 +696,36 @@ static void collect_rename_info(struct merge_options *opt,
 	struct rename_info *renames = &opt->priv->renames;
 	unsigned side;
 
+	/*
+	 * Update dir_rename_mask (determines ignore-rename-source validity)
+	 *
+	 * dir_rename_mask helps us keep track of when directory rename
+	 * detection may be relevant.  Basically, whenver a directory is
+	 * removed on one side of history, and a file is added to that
+	 * directory on the other side of history, directory rename
+	 * detection is relevant (meaning we have to detect renames for all
+	 * files within that directory to deduce where the directory
+	 * moved).  Also, whenever a directory needs directory rename
+	 * detection, due to the "majority rules" choice for where to move
+	 * it (see t6423 testcase 1f), we also need to detect renames for
+	 * all files within subdirectories of that directory as well.
+	 *
+	 * Here we haven't looked at files within the directory yet, we are
+	 * just looking at the directory itself.  So, if we aren't yet in
+	 * a case where a parent directory needed directory rename detection
+	 * (i.e. dir_rename_mask != 0x07), and if the directory was removed
+	 * on one side of history, record the mask of the other side of
+	 * history in dir_rename_mask.
+	 */
+	if (renames->dir_rename_mask != 0x07 &&
+	    (dirmask == 3 || dirmask == 5)) {
+		/* simple sanity check */
+		assert(renames->dir_rename_mask == 0 ||
+		       renames->dir_rename_mask == (dirmask & ~1));
+		/* update dir_rename_mask; have it record mask of new side */
+		renames->dir_rename_mask = (dirmask & ~1);
+	}
+
 	/* Update dirs_removed, as needed */
 	if (dirmask == 1 || dirmask == 3 || dirmask == 5) {
 		/* absent_mask = 0x07 - dirmask; sides = absent_mask/2 */
@@ -699,12 +745,14 @@ static void collect_rename_info(struct merge_options *opt,
 		/* Check for deletion on side */
 		if ((filemask & 1) && !(filemask & side_mask))
 			add_pair(opt, names, fullname, side, 0 /* delete */,
-				 match_mask & filemask);
+				 match_mask & filemask,
+				 renames->dir_rename_mask);
 
 		/* Check for addition on side */
 		if (!(filemask & 1) && (filemask & side_mask))
 			add_pair(opt, names, fullname, side, 1 /* add */,
-				 match_mask & filemask);
+				 match_mask & filemask,
+				 renames->dir_rename_mask);
 	}
 }
 
@@ -722,12 +770,14 @@ static int collect_merge_info_callback(int n,
 	 */
 	struct merge_options *opt = info->data;
 	struct merge_options_internal *opti = opt->priv;
+	struct rename_info *renames = &opt->priv->renames;
 	struct string_list_item pi;  /* Path Info */
 	struct conflict_info *ci; /* typed alias to pi.util (which is void*) */
 	struct name_entry *p;
 	size_t len;
 	char *fullpath;
 	const char *dirname = opti->current_dir_name;
+	unsigned prev_dir_rename_mask = renames->dir_rename_mask;
 	unsigned filemask = mask & ~dirmask;
 	unsigned match_mask = 0; /* will be updated below */
 	unsigned mbase_null = !(mask & 1);
@@ -868,8 +918,13 @@ static int collect_merge_info_callback(int n,
 
 		original_dir_name = opti->current_dir_name;
 		opti->current_dir_name = pi.string;
-		ret = traverse_trees(NULL, 3, t, &newinfo);
+		if (renames->dir_rename_mask == 0 ||
+		    renames->dir_rename_mask == 0x07)
+			ret = traverse_trees(NULL, 3, t, &newinfo);
+		else
+			ret = traverse_trees_wrapper(NULL, 3, t, &newinfo);
 		opti->current_dir_name = original_dir_name;
+		renames->dir_rename_mask = prev_dir_rename_mask;
 
 		for (i = MERGE_BASE; i <= MERGE_SIDE2; i++)
 			free(buf[i]);

-- 
gitgitgadget

Elijah Newren via GitGitGadget· Feb 28, 2021, 03:58 UTC · re: Elijah Newren via GitGitGadget · lore

[PATCH 6/8] merge-ort: use relevant_sources to filter possible rename sources

From: Elijah Newren <newren@gmail.com>

The past several commits determined conditions when rename sources might be needed, and filled a relevant_sources strset with those paths. Pass these along to diffcore_rename_extended() to use to limit the sources that we need to detect renames for.

For the testcases mentioned in commit 557ac0350d ("merge-ort: begin performance work; instrument with trace2_region_* calls", 2020-10-28), this change improves the performance as follows:

                            Before                  After
    no-renames:       12.596 s ±  0.061 s     6.003 s ±  0.048 s
    mega-renames:    130.465 s ±  0.259 s   114.009 s ±  0.236 s
    just-one-mega:     3.958 s ±  0.010 s     3.489 s ±  0.017 s

Signed-off-by: Elijah Newren <newren@gmail.com>
---
 merge-ort.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Show changes to merge-ort.c +1 −1

diff --git a/merge-ort.c b/merge-ort.c
index 27acaa7380be..66892c63cee2 100644
--- a/merge-ort.c
+++ b/merge-ort.c
@@ -2209,7 +2209,7 @@ static void detect_regular_renames(struct merge_options *opt,
 	diff_queued_diff = renames->pairs[side_index];
 	trace2_region_enter("diff", "diffcore_rename", opt->repo);
 	diffcore_rename_extended(&diff_opts,
-				 NULL,
+				 &renames->relevant_sources[side_index],
 				 &renames->dirs_removed[side_index],
 				 &renames->dir_rename_count[side_index]);
 	trace2_region_leave("diff", "diffcore_rename", opt->repo);

-- 
gitgitgadget

Elijah Newren via GitGitGadget· Feb 28, 2021, 03:58 UTC · re: Elijah Newren via GitGitGadget · lore

[PATCH 7/8] merge-ort: skip rename detection entirely if possible

From: Elijah Newren <newren@gmail.com>

diffcore_rename_extended() will do a bunch of setup, then check for
exact renames, then abort before inexact rename detection if there are
no more sources or destinations that need to be matched.  It will
sometimes be the case, however, that either
  * we start with neither any sources or destinations
  * we start with no *relevant* sources
In the first of these two cases, the setup and exact rename detection
will be very cheap since there are 0 files to operate on.  In the second
case, it is quite possible to have thousands of files with none of the
source ones being relevant.  Avoid calling diffcore_rename_extended() or
even some of the setup before diffcore_rename_extended() when we can
determine that rename detection is unnecessary.

For the testcases mentioned in commit 557ac0350d ("merge-ort: begin performance work; instrument with trace2_region_* calls", 2020-10-28), this change improves the performance as follows:

                            Before                  After
    no-renames:        6.003 s ±  0.048 s     5.708 s ±  0.111 s
    mega-renames:    114.009 s ±  0.236 s   102.171 s ±  0.440 s
    just-one-mega:     3.489 s ±  0.017 s     3.471 s ±  0.015 s

Signed-off-by: Elijah Newren <newren@gmail.com>
---
 merge-ort.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)

Show changes to merge-ort.c +45 −0

diff --git a/merge-ort.c b/merge-ort.c
index 66892c63cee2..8602c7b8936f 100644
--- a/merge-ort.c
+++ b/merge-ort.c
@@ -2158,6 +2158,19 @@ static int process_renames(struct merge_options *opt,
 	return clean_merge;
 }
 
+static inline int possible_side_renames(struct rename_info *renames,
+					unsigned side_index)
+{
+	return renames->pairs[side_index].nr > 0 &&
+	       !strset_empty(&renames->relevant_sources[side_index]);
+}
+
+static inline int possible_renames(struct rename_info *renames)
+{
+	return possible_side_renames(renames, 1) ||
+	       possible_side_renames(renames, 2);
+}
+
 static void resolve_diffpair_statuses(struct diff_queue_struct *q)
 {
 	/*
@@ -2194,6 +2207,16 @@ static void detect_regular_renames(struct merge_options *opt,
 	struct diff_options diff_opts;
 	struct rename_info *renames = &opt->priv->renames;
 
+	if (!possible_side_renames(renames, side_index)) {
+		/*
+		 * No rename detection needed for this side, but we still need
+		 * to make sure 'adds' are marked correctly in case the other
+		 * side had directory renames.
+		 */
+		resolve_diffpair_statuses(&renames->pairs[side_index]);
+		return;
+	}
+
 	repo_diff_setup(opt->repo, &diff_opts);
 	diff_opts.flags.recursive = 1;
 	diff_opts.flags.rename_empty = 0;
@@ -2311,6 +2334,8 @@ static int detect_and_process_renames(struct merge_options *opt,
 	int need_dir_renames, s, clean = 1;
 
 	memset(&combined, 0, sizeof(combined));
+	if (!possible_renames(renames))
+		goto cleanup;
 
 	trace2_region_enter("merge", "regular renames", opt->repo);
 	detect_regular_renames(opt, MERGE_SIDE1);
@@ -2345,6 +2370,26 @@ static int detect_and_process_renames(struct merge_options *opt,
 	clean &= process_renames(opt, &combined);
 	trace2_region_leave("merge", "process renames", opt->repo);
 
+	goto simple_cleanup; /* collect_renames() handles some of cleanup */
+
+cleanup:
+	/*
+	 * Free now unneeded filepairs, which would have been handled
+	 * in collect_renames() normally but we're about to skip that
+	 * code...
+	 */
+	for (s = MERGE_SIDE1; s <= MERGE_SIDE2; s++) {
+		struct diff_queue_struct *side_pairs;
+		int i;
+
+		side_pairs = &renames->pairs[s];
+		for (i = 0; i < side_pairs->nr; ++i) {
+			struct diff_filepair *p = side_pairs->queue[i];
+			diff_free_filepair(p);
+		}
+	}
+
+simple_cleanup:
 	/* Free memory for renames->pairs[] and combined */
 	for (s = MERGE_SIDE1; s <= MERGE_SIDE2; s++) {
 		free(renames->pairs[s].queue);

-- 
gitgitgadget

Elijah Newren via GitGitGadget· Feb 28, 2021, 03:58 UTC · re: Elijah Newren via GitGitGadget · lore

[PATCH 8/8] diffcore-rename: avoid doing basename comparisons for irrelevant sources

From: Elijah Newren <newren@gmail.com>

The basename comparison optimization implemented in find_basename_matches() is very beneficial since it allows a source to sometimes only be compared with one other file instead of N other files. When a match is found, both a source and destination can be removed from the matrix of inexact rename comparisons. In contrast, the irrelevant source optimization only allows us to remove a source from the matrix of inexact rename comparisons...but it has the advantage of allowing a source file to not even be loaded into memory at all and be compared to 0 other files. Generally, not even comparing is a bigger performance win, so when both optimizations could apply, prefer to use the irrelevant-source optimization.

For the testcases mentioned in commit 557ac0350d ("merge-ort: begin performance work; instrument with trace2_region_* calls", 2020-10-28), this change improves the performance as follows:

                            Before                  After
    no-renames:        5.708 s ±  0.111 s     5.680 s ±  0.096 s
    mega-renames:    102.171 s ±  0.440 s    13.812 s ±  0.162 s
    just-one-mega:     3.471 s ±  0.015 s   506.0  ms ±  3.9  ms

Signed-off-by: Elijah Newren <newren@gmail.com>
---
 diffcore-rename.c | 37 +++++++++++++++++++++++++++++++++----
 1 file changed, 33 insertions(+), 4 deletions(-)

Show changes to diffcore-rename.c +33 −4

diff --git a/diffcore-rename.c b/diffcore-rename.c
index 7f6115fd9018..e8508541be14 100644
--- a/diffcore-rename.c
+++ b/diffcore-rename.c
@@ -527,6 +527,7 @@ static void update_dir_rename_counts(struct dir_rename_info *info,
 }
 
 static void initialize_dir_rename_info(struct dir_rename_info *info,
+				       struct strset *relevant_sources,
 				       struct strset *dirs_removed,
 				       struct strmap *dir_rename_count)
 {
@@ -534,7 +535,7 @@ static void initialize_dir_rename_info(struct dir_rename_info *info,
 	struct strmap_entry *entry;
 	int i;
 
-	if (!dirs_removed) {
+	if (!dirs_removed && !relevant_sources) {
 		info->setup = 0;
 		return;
 	}
@@ -549,7 +550,20 @@ static void initialize_dir_rename_info(struct dir_rename_info *info,
 	strmap_init_with_options(&info->dir_rename_guess, NULL, 0);
 
 	/* Setup info->relevant_source_dirs */
-	info->relevant_source_dirs = dirs_removed;
+	info->relevant_source_dirs = NULL;
+	if (dirs_removed || !relevant_sources) {
+		info->relevant_source_dirs = dirs_removed; /* might be NULL */
+	} else {
+		info->relevant_source_dirs = xmalloc(sizeof(struct strintmap));
+		strset_init(info->relevant_source_dirs);
+		strset_for_each_entry(relevant_sources, &iter, entry) {
+			char *dirname = get_dirname(entry->key);
+			if (!dirs_removed ||
+			    strset_contains(dirs_removed, dirname))
+				strset_add(info->relevant_source_dirs, dirname);
+			free(dirname);
+		}
+	}
 
 	/*
 	 * Loop setting up both info->idx_map, and doing setup of
@@ -627,6 +641,13 @@ static void cleanup_dir_rename_info(struct dir_rename_info *info,
 	/* dir_rename_guess */
 	strmap_clear(&info->dir_rename_guess, 1);
 
+	/* relevant_source_dirs */
+	if (info->relevant_source_dirs &&
+	    info->relevant_source_dirs != dirs_removed) {
+		strset_clear(info->relevant_source_dirs);
+		FREE_AND_NULL(info->relevant_source_dirs);
+	}
+
 	/* dir_rename_count */
 	if (!keep_dir_rename_count) {
 		partial_clear_dir_rename_count(info->dir_rename_count);
@@ -749,6 +770,7 @@ static int idx_possible_rename(char *filename, struct dir_rename_info *info)
 static int find_basename_matches(struct diff_options *options,
 				 int minimum_score,
 				 struct dir_rename_info *info,
+				 struct strset *relevant_sources,
 				 struct strset *dirs_removed)
 {
 	/*
@@ -839,6 +861,11 @@ static int find_basename_matches(struct diff_options *options,
 		intptr_t src_index;
 		intptr_t dst_index;
 
+		/* Skip irrelevant sources */
+		if (relevant_sources &&
+		    !strset_contains(relevant_sources, filename))
+			continue;
+
 		/*
 		 * If the basename is unique among remaining sources, then
 		 * src_index will equal 'i' and we can attempt to match it
@@ -1164,7 +1191,7 @@ void diffcore_rename_extended(struct diff_options *options,
 
 		/* Preparation for basename-driven matching. */
 		trace2_region_enter("diff", "dir rename setup", options->repo);
-		initialize_dir_rename_info(&info,
+		initialize_dir_rename_info(&info, relevant_sources,
 					   dirs_removed, dir_rename_count);
 		trace2_region_leave("diff", "dir rename setup", options->repo);
 
@@ -1172,7 +1199,9 @@ void diffcore_rename_extended(struct diff_options *options,
 		trace2_region_enter("diff", "basename matches", options->repo);
 		rename_count += find_basename_matches(options,
 						      min_basename_score,
-						      &info, dirs_removed);
+						      &info,
+						      relevant_sources,
+						      dirs_removed);
 		trace2_region_leave("diff", "basename matches", options->repo);
 
 		/*

-- 
gitgitgadget

Elijah Newren· Mar 1, 2021, 16:39 UTC · re: Elijah Newren via GitGitGadget · lore

Re: [PATCH 0/8] Optimization batch 9: avoid detecting irrelevant renames

On Sat, Feb 27, 2021 at 7:58 PM Elijah Newren via GitGitGadget <gitgitgadget@gmail.com> wrote:

Show 94 quoted lines

>
> This series depends textually on ort-perf-batch-8, but semantically it's
> almost completely unrelated and can be reviewed without any familiarity with
> any of the previous patch series.
>
> === Basic Optimization idea ===
>
> This series determines paths which meet special cases where detection of
> renames is irrelevant, where the irrelevance is due to the fact that the
> merge machinery will arrive at the same result regardless of whether a
> rename is detected for any of those paths. This series represents
> "Optimization #2" from my Git Merge 2020 talk[1], though this series has
> some improvements on the optimization relative to what I had at that time.
>
> The basic idea here is that if side A of history:
>
>  * only modifies/adds/deletes a few files
>  * adds new files to few if any of the directories that side B deleted or
>    renamed
>
> then when we do rename detection on side B we can avoid even looking at most
> (and perhaps even all) paths that side B deleted. Since commits being
> rebased or cherry-picked tend to only modify a few files, this optimization
> tends to be particularly effective for rebases and cherry-picks.
>
> Basing rename detection on what the other side of history did to a file
> means that extra information needs to be fed from merge-ort to
> diffcore-rename in order to take advantage of such an optimization.
>
> === Comparison to previous series ===
>
> This series differs from my two previous optimizations[2][3] (focusing on
> basename-guided rename detection) in two important aspects:
>
>  * there are no behavioral changes (there is no heuristic involved)
>
>  * this optimization is merge specific (it does not help the diff/status/log
>    family of commands, just merge/rebase/cherry-pick and such)
>
> === Results ===
>
> For the testcases mentioned in commit 557ac0350d ("merge-ort: begin
> performance work; instrument with trace2_region_* calls", 2020-10-28), the
> changes in just this series improves the performance as follows:
>
>                      Before Series           After Series
> no-renames:       12.596 s ±  0.061 s     5.680 s ±  0.096 s
> mega-renames:    130.465 s ±  0.259 s    13.812 s ±  0.162 s
> just-one-mega:     3.958 s ±  0.010 s   506.0  ms ±  3.9  ms
>
>
> However, interestingly, if we had ignored the basename-guided rename
> detection optimizations[2][3], then this optimization series would have
> improved the performance as follows:
>
>                Before Basename Series   After Just This Series
> no-renames:      13.815 s ±  0.062 s      5.728 s ±  0.104 s
> mega-renames:  1799.937 s ±  0.493 s     18.213 s ±  0.139 s
> just-one-mega    51.289 s ±  0.019 s    891.9  ms ±  7.0  ms
>
>
> As a reminder, before any merge-ort/diffcore-rename performance work, the
> performance results we started with (as noted in the same commit message)
> were:
>
> no-renames-am:      6.940 s ±  0.485 s
> no-renames:        18.912 s ±  0.174 s
> mega-renames:    5964.031 s ± 10.459 s
> just-one-mega:    149.583 s ±  0.751 s
>
>
> === Competition between optimizations ===
>
> We now have three major rename-related optimizations:
>
>  * exact rename detection
>  * basename-guided rename detection[2][3]
>  * skip-because-unnecessary (this series)
>
> It is possible for all three to potentially apply for specific paths (they
> do for the majority of renamed paths in our testcases), but we cannot use
> more than one for any given path. It turns out that the priority we give
> each optimization is very important and can drastically affect performance.
> We get best results by prioritizing them as follows:
>
>  1. exact rename detection
>  2. skip-because-unnecessary
>  3. basename-guided rename detection
>
> The third-to-last patch of this series also discusses this ordering and
> another minor variant of the skip-because-unnecessary optimization that was
> tried (and resulted in less effective performance gains than reported here),
> as well as some of the preparatory work over the past few years that this
> series relies on in order to enable this optimization.

Oops. When I restructured the series I carefully re-read the commit messages to make sure I didn't forget to update one...but I apparently forgot to update the cover letter. The discussion was actually split across a few patches by the refactoring, and what is now the third-to-last patch doesn't contain any of that discussion.

Show 48 quoted lines

> === Near optimal? ===
>
> You may remember that there was a row labelled "everything else" from the
> commit message of 557ac0350d that represented the maximum possible speed-up
> from accelerating rename detection alone; as stated in that commit, those
> rows represented how fast the code could be if we had somehow infinitely
> parallelized the inexact rename detection. However, if you compare those
> "maximum speedup" numbers to what we have above, you'll note that the
> infinitely parallelized inexact rename detection would have been slightly
> slower than the results we have now achieved. (The reason this is possible,
> despite the fact that we still spend time in rename detection after our
> optimizations, is because we implemented two optimizations outside of
> diffcore_rename() along the way.) However, this good news does also come
> with a downside -- it means that our remaining optimization potential is
> somewhat limited, and subsequent optimization series will have to fight for
> much smaller gains.
>
> [1]
> https://github.com/newren/presentations/blob/pdfs/merge-performance/merge-performance-slides.pdf
> [2]
> https://lore.kernel.org/git/pull.843.git.1612651937.gitgitgadget@gmail.com/
> [3]
> https://lore.kernel.org/git/pull.844.git.1613289544.gitgitgadget@gmail.com/
>
> Elijah Newren (8):
>   diffcore-rename: enable filtering possible rename sources
>   merge-ort: precompute subset of sources for which we need rename
>     detection
>   merge-ort: add data structures for an alternate tree traversal
>   merge-ort: introduce wrappers for alternate tree traversal
>   merge-ort: precompute whether directory rename detection is needed
>   merge-ort: use relevant_sources to filter possible rename sources
>   merge-ort: skip rename detection entirely if possible
>   diffcore-rename: avoid doing basename comparisons for irrelevant
>     sources
>
>  diffcore-rename.c |  63 ++++++++++---
>  diffcore.h        |   1 +
>  merge-ort.c       | 236 +++++++++++++++++++++++++++++++++++++++++++++-
>  3 files changed, 285 insertions(+), 15 deletions(-)
>
>
> base-commit: 4be565c472088d4144063b736308bf2a57331f45
> Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-845%2Fnewren%2Fort-perf-batch-9-v1
> Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-845/newren/ort-perf-batch-9-v1
> Pull-Request: https://github.com/gitgitgadget/git/pull/845
> --
> gitgitgadget

Elijah Newren· Mar 4, 2021, 07:54 UTC · re: Elijah Newren via GitGitGadget · lore

Re: [PATCH 0/8] Optimization batch 9: avoid detecting irrelevant renames

Hi,

On Sat, Feb 27, 2021 at 7:58 PM Elijah Newren via GitGitGadget <gitgitgadget@gmail.com> wrote:

Show 17 quoted lines

>
> This series depends textually on ort-perf-batch-8, but semantically it's
> almost completely unrelated and can be reviewed without any familiarity with
> any of the previous patch series.
>
> === Basic Optimization idea ===
>
> The basic idea here is that if side A of history:
>
>  * only modifies/adds/deletes a few files
>  * adds new files to few if any of the directories that side B deleted or
>    renamed
>
> then when we do rename detection on side B we can avoid even looking at most
> (and perhaps even all) paths that side B deleted. Since commits being
> rebased or cherry-picked tend to only modify a few files, this optimization
> tends to be particularly effective for rebases and cherry-picks.

After thinking it over a bit more, there's a much better way to put this summary:

    We only need expensive rename detection on the subset of files
changed on *both* sides (for the most part).

This is because:

1. The primary reason for rename detection in merges is enabling
three-way content merges
2. The purpose of three-way content merges is reconciling changes when
*both* sides of history modified some file
3. If a file was only modified by the side that renamed the file, then
detecting the rename is irrelevant; we'll get the same answer without
knowing about the rename.
4. (Well...there are rare cases where we need the rename for reasons
other than three-way content merges.  Patch 5 explains those.)

Elijah Newren via GitGitGadget· Mar 9, 2021, 00:09 UTC · re: Elijah Newren via GitGitGadget · lore

[PATCH v2 0/8] Optimization batch 9: avoid detecting irrelevant renames

This series depends textually on ort-perf-batch-8, but semantically it's almost completely unrelated and can be reviewed without any familiarity with any of the previous patch series.

There are no changes since v1; it's just a resend just over a week later to bump it so it isn't lost.

=== Basic Optimization idea ===

The basic idea here is:

We only need expensive rename detection on the subset of files changed on both sides of history (for the most part).

This is because:

 1. The primary reason for rename detection in merges is enabling three-way
    content merges
 2. The purpose of three-way content merges is reconciling changes when

both sides of history modified some file 3. If a file was only modified by the side that renamed the file, then detecting the rename is irrelevant; we'll get the same answer without knowing about the rename. 4. (Well...there are rare cases where we need the rename for reasons other than three-way content merges. Patch 5 explains those.)

Since commits being rebased or cherry-picked tend to only modify a few files, this optimization tends to be particularly effective for rebases and cherry-picks.

=== Comparison to previous series ===

This series differs from my two previous optimizations[2][3] (focusing on basename-guided rename detection) in two important aspects:

 * there are no behavioral changes (there is no heuristic involved)
 * this optimization is merge specific (it does not help the diff/status/log
   family of commands, just merge/rebase/cherry-pick and such)

=== Results ===

                     Before Series           After Series
no-renames:       12.596 s ±  0.061 s     5.680 s ±  0.096 s
mega-renames:    130.465 s ±  0.259 s    13.812 s ±  0.162 s
just-one-mega:     3.958 s ±  0.010 s   506.0  ms ±  3.9  ms

However, interestingly, if we had ignored the basename-guided rename detection optimizations[2][3], then this optimization series would have improved the performance as follows:

               Before Basename Series   After Just This Series
no-renames:      13.815 s ±  0.062 s      5.728 s ±  0.104 s
mega-renames:  1799.937 s ±  0.493 s     18.213 s ±  0.139 s
just-one-mega    51.289 s ±  0.019 s    891.9  ms ±  7.0  ms

As a reminder, before any merge-ort/diffcore-rename performance work, the performance results we started with (as noted in the same commit message) were:

no-renames-am: 6.940 s ± 0.485 s no-renames: 18.912 s ± 0.174 s mega-renames: 5964.031 s ± 10.459 s just-one-mega: 149.583 s ± 0.751 s

=== Competition between optimizations ===

We now have three major rename-related optimizations:

 * exact rename detection
 * basename-guided rename detection[2][3]
 * skip-because-unnecessary (this series)

 1. exact rename detection
 2. skip-because-unnecessary
 3. basename-guided rename detection

Some of the commit messages discuss this ordering and another minor variant of the skip-because-unnecessary optimization that was tried (and resulted in less effective performance gains than reported here), as well as some of the preparatory work over the past few years that this series relies on in order to enable this optimization.

=== Near optimal? ===

Elijah Newren (8):
  diffcore-rename: enable filtering possible rename sources
  merge-ort: precompute subset of sources for which we need rename
    detection
  merge-ort: add data structures for an alternate tree traversal
  merge-ort: introduce wrappers for alternate tree traversal
  merge-ort: precompute whether directory rename detection is needed
  merge-ort: use relevant_sources to filter possible rename sources
  merge-ort: skip rename detection entirely if possible
  diffcore-rename: avoid doing basename comparisons for irrelevant
    sources

 diffcore-rename.c |  63 ++++++++++---
 diffcore.h        |   1 +
 merge-ort.c       | 236 +++++++++++++++++++++++++++++++++++++++++++++-
 3 files changed, 285 insertions(+), 15 deletions(-)

base-commit: 4be565c472088d4144063b736308bf2a57331f45
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-845%2Fnewren%2Fort-perf-batch-9-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-845/newren/ort-perf-batch-9-v2
Pull-Request: https://github.com/gitgitgadget/git/pull/845

Range-diff vs v1:

 1:  064fa5de1e20 = 1:  dab8e3c6aee5 diffcore-rename: enable filtering possible rename sources
 2:  69b42a41e83a = 2:  33c231331744 merge-ort: precompute subset of sources for which we need rename detection
 3:  042ce66011ef = 3:  89b43c9f75a0 merge-ort: add data structures for an alternate tree traversal
 4:  7673e4c23bbb = 4:  6497050c0012 merge-ort: introduce wrappers for alternate tree traversal
 5:  8dbf0a452545 = 5:  608d5a4c6ad7 merge-ort: precompute whether directory rename detection is needed
 6:  6b20977a5a81 = 6:  d62fdee45ad3 merge-ort: use relevant_sources to filter possible rename sources
 7:  d5486ab28462 = 7:  cd931286f24d merge-ort: skip rename detection entirely if possible
 8:  8fed92b62f37 = 8:  c443ba8abb89 diffcore-rename: avoid doing basename comparisons for irrelevant sources

-- 
gitgitgadget

Elijah Newren via GitGitGadget· Mar 9, 2021, 00:09 UTC · re: Elijah Newren via GitGitGadget · lore

[PATCH v2 2/8] merge-ort: precompute subset of sources for which we need rename detection

From: Elijah Newren <newren@gmail.com>

To see why, first note that the merge machinery uses detected renames in two ways:

   * directory rename detection: when one side of history renames a
       directory, and the other side of history adds new files to that
       directory, we want to be able to warn the user about the need to
       chose whether those new files stay in the old directory or move
       to the new one.

   * three-way content merging: in order to do three-way content merging
       of files, we need three different file versions.  If one side of
       history renamed a file, then some of the content for the file is
       found under a different path than in the merge base or on the
       other side of history.

This commit concentrates just on the three-way content merging; it will punt and mark all sources as needed for directory rename detection, and leave it to future commits to narrow that down more.

The point of three-way content merging is to reconcile changes made on *both* sides of history. What if the file wasn't modified on both sides? There are two possibilities:

   * If it wasn't modified on the renamed side:
       -> then we get to do exact rename detection, which is cheap.

   * If it wasn't modified on the unrenamed side:
       -> then detection of a rename for that source file is irrelevant

                 old.c     new.c
   MERGE_BASE:   01d01d    000000
   MERGE_SIDE1:  01d01d    000000
   MERGE_SIDE2:  000000    5e1ec7

If the rename *isn't* detected:
   then old.c looks like it was unmodified on one side and deleted on
   the other and should thus be removed.  new.c looks like a new file we
   should keep as-is.

If the rename *is* detected:
   then a three-way content merge is done.  Since the version of the
   file in MERGE_BASE and MERGE_SIDE1 are identical, the three-way merge
   will produce exactly the version of the file whose abbreviated
   object id is 5e1ec7.  It will record that file at the path new.c,
   while removing old.c from the directory.

Use this information to compute whether we need rename detection for each source created in add_pair().

 * bringing consistency to add/add, rename/add, and rename/rename
    conflict types, as done back in the topic merged at commit
    ac193e0e0a ("Merge branch 'en/merge-path-collision'", 2019-01-04),
    and further extended in commits 2a7c16c980 ("t6422, t6426: be more
    flexible for add/add conflicts involving renames", 2020-08-10) and
    e8eb99d4a6 ("t642[23]: be more flexible for add/add conflicts
    involving pair renames", 2020-08-10)

  * making rename/delete more consistent with modify/delete
    as done in commits 1f3c9ba707 ("t6425: be more flexible with
    rename/delete conflict messages", 2020-08-10) and 727c75b23f
    ("t6404, t6423: expect improved rename/delete handling in ort
    backend", 2020-10-26)

Signed-off-by: Elijah Newren <newren@gmail.com>
---
 merge-ort.c | 35 ++++++++++++++++++++++++++++++++---
 1 file changed, 32 insertions(+), 3 deletions(-)

Show changes to merge-ort.c +32 −3

diff --git a/merge-ort.c b/merge-ort.c
index aba0b9fa54c3..83aa4c08121f 100644
--- a/merge-ort.c
+++ b/merge-ort.c
@@ -88,6 +88,20 @@ struct rename_info {
 	 */
 	struct strmap dir_renames[3];
 
+	/*
+	 * relevant_sources: deleted paths for which we need rename detection
+	 *
+	 * relevant_sources is a set of deleted paths on each side of
+	 * history for which we need rename detection.  If a path is deleted
+	 * on one side of history, we need to detect if it is part of a
+	 * rename if either
+	 *    * we need to detect renames for an ancestor directory
+	 *    * the file is modified/deleted on the other side of history
+	 * If neither of those are true, we can skip rename detection for
+	 * that path.
+	 */
+	struct strset relevant_sources[3];
+
 	/*
 	 * needed_limit: value needed for inexact rename detection to run
 	 *
@@ -358,6 +372,8 @@ static void clear_or_reinit_internal_opts(struct merge_options_internal *opti,
 			strmap_clear(&renames->dir_rename_count[i], 1);
 
 		strmap_func(&renames->dir_renames[i], 0);
+
+		strset_func(&renames->relevant_sources[i]);
 	}
 
 	if (!reinitialize) {
@@ -533,12 +549,21 @@ static void add_pair(struct merge_options *opt,
 		     struct name_entry *names,
 		     const char *pathname,
 		     unsigned side,
-		     unsigned is_add /* if false, is_delete */)
+		     unsigned is_add /* if false, is_delete */,
+		     unsigned match_mask)
 {
 	struct diff_filespec *one, *two;
 	struct rename_info *renames = &opt->priv->renames;
 	int names_idx = is_add ? side : 0;
 
+	if (!is_add) {
+		unsigned content_relevant = (match_mask == 0);
+		unsigned location_relevant = 1; /* FIXME: compute this */
+
+		if (content_relevant || location_relevant)
+			strset_add(&renames->relevant_sources[side], pathname);
+	}
+
 	one = alloc_filespec(pathname);
 	two = alloc_filespec(pathname);
 	fill_filespec(is_add ? two : one,
@@ -575,11 +600,13 @@ static void collect_rename_info(struct merge_options *opt,
 
 		/* Check for deletion on side */
 		if ((filemask & 1) && !(filemask & side_mask))
-			add_pair(opt, names, fullname, side, 0 /* delete */);
+			add_pair(opt, names, fullname, side, 0 /* delete */,
+				 match_mask & filemask);
 
 		/* Check for addition on side */
 		if (!(filemask & 1) && (filemask & side_mask))
-			add_pair(opt, names, fullname, side, 1 /* add */);
+			add_pair(opt, names, fullname, side, 1 /* add */,
+				 match_mask & filemask);
 	}
 }
 
@@ -3228,6 +3255,8 @@ static void merge_start(struct merge_options *opt, struct merge_result *result)
 					 NULL, 1);
 		strmap_init_with_options(&renames->dir_renames[i],
 					 NULL, 0);
+		strset_init_with_options(&renames->relevant_sources[i],
+					 NULL, 0);
 	}
 
 	/*

-- 
gitgitgadget

Elijah Newren via GitGitGadget· Mar 9, 2021, 00:09 UTC · re: Elijah Newren via GitGitGadget · lore

[PATCH v2 1/8] diffcore-rename: enable filtering possible rename sources

From: Elijah Newren <newren@gmail.com>

There are two important pieces to this optimization that may not be obvious at first glance:

  * We do not require callers to just filter the filepairs out
    to remove the non-relevant sources, because exact rename detection
    is fast and when it finds a match it can remove both a source and a
    destination whereas the relevant_sources filter can only remove a
    source.

  * We need to filter out the source pairs in a preliminary pass instead
    of adding a
       strset_contains(relevant_sources, one->path)
    check within the nested matrix loop.  The reason for that is if we
    have 30k renames, doing 30k * 30k = 900M strset_contains() calls
    becomes extraordinarily expensive and defeats the performance gains
    from this change; we only want to do 30k such calls instead.

Signed-off-by: Elijah Newren <newren@gmail.com>
---
 diffcore-rename.c | 26 +++++++++++++++++++-------
 diffcore.h        |  1 +
 merge-ort.c       |  1 +
 3 files changed, 21 insertions(+), 7 deletions(-)

Show changes to 3 files +21 −7

diffcore-rename.c, diffcore.h, merge-ort.c

diff --git a/diffcore-rename.c b/diffcore-rename.c
index 1fe902ed2af0..7f6115fd9018 100644
--- a/diffcore-rename.c
+++ b/diffcore-rename.c
@@ -991,11 +991,12 @@ static int find_renames(struct diff_score *mx,
 	return count;
 }
 
-static void remove_unneeded_paths_from_src(int detecting_copies)
+static void remove_unneeded_paths_from_src(int detecting_copies,
+					   struct strset *interesting)
 {
 	int i, new_num_src;
 
-	if (detecting_copies)
+	if (detecting_copies && !interesting)
 		return; /* nothing to remove */
 	if (break_idx)
 		return; /* culling incompatible with break detection */
@@ -1022,12 +1023,18 @@ static void remove_unneeded_paths_from_src(int detecting_copies)
 	 *      from rename_src here.
 	 */
 	for (i = 0, new_num_src = 0; i < rename_src_nr; i++) {
+		struct diff_filespec *one = rename_src[i].p->one;
+
 		/*
 		 * renames are stored in rename_dst, so if a rename has
 		 * already been detected using this source, we can just
 		 * remove the source knowing rename_dst has its info.
 		 */
-		if (rename_src[i].p->one->rename_used)
+		if (!detecting_copies && one->rename_used)
+			continue;
+
+		/* If we don't care about the source path, skip it */
+		if (interesting && !strset_contains(interesting, one->path))
 			continue;
 
 		if (new_num_src < i)
@@ -1040,6 +1047,7 @@ static void remove_unneeded_paths_from_src(int detecting_copies)
 }
 
 void diffcore_rename_extended(struct diff_options *options,
+			      struct strset *relevant_sources,
 			      struct strset *dirs_removed,
 			      struct strmap *dir_rename_count)
 {
@@ -1060,6 +1068,8 @@ void diffcore_rename_extended(struct diff_options *options,
 	want_copies = (detect_rename == DIFF_DETECT_COPY);
 	if (dirs_removed && (break_idx || want_copies))
 		BUG("dirs_removed incompatible with break/copy detection");
+	if (break_idx && relevant_sources)
+		BUG("break detection incompatible with source specification");
 	if (!minimum_score)
 		minimum_score = DEFAULT_RENAME_SCORE;
 
@@ -1127,9 +1137,10 @@ void diffcore_rename_extended(struct diff_options *options,
 		/*
 		 * Cull sources:
 		 *   - remove ones corresponding to exact renames
+		 *   - remove ones not found in relevant_sources
 		 */
 		trace2_region_enter("diff", "cull after exact", options->repo);
-		remove_unneeded_paths_from_src(want_copies);
+		remove_unneeded_paths_from_src(want_copies, relevant_sources);
 		trace2_region_leave("diff", "cull after exact", options->repo);
 	} else {
 		/* Determine minimum score to match basenames */
@@ -1148,7 +1159,7 @@ void diffcore_rename_extended(struct diff_options *options,
 		 *   - remove ones involved in renames (found via exact match)
 		 */
 		trace2_region_enter("diff", "cull after exact", options->repo);
-		remove_unneeded_paths_from_src(want_copies);
+		remove_unneeded_paths_from_src(want_copies, NULL);
 		trace2_region_leave("diff", "cull after exact", options->repo);
 
 		/* Preparation for basename-driven matching. */
@@ -1167,9 +1178,10 @@ void diffcore_rename_extended(struct diff_options *options,
 		/*
 		 * Cull sources, again:
 		 *   - remove ones involved in renames (found via basenames)
+		 *   - remove ones not found in relevant_sources
 		 */
 		trace2_region_enter("diff", "cull basename", options->repo);
-		remove_unneeded_paths_from_src(want_copies);
+		remove_unneeded_paths_from_src(want_copies, relevant_sources);
 		trace2_region_leave("diff", "cull basename", options->repo);
 	}
 
@@ -1342,5 +1354,5 @@ void diffcore_rename_extended(struct diff_options *options,
 
 void diffcore_rename(struct diff_options *options)
 {
-	diffcore_rename_extended(options, NULL, NULL);
+	diffcore_rename_extended(options, NULL, NULL, NULL);
 }
diff --git a/diffcore.h b/diffcore.h
index c6ba64abd198..737c93a6cc79 100644
--- a/diffcore.h
+++ b/diffcore.h
@@ -166,6 +166,7 @@ void partial_clear_dir_rename_count(struct strmap *dir_rename_count);
 void diffcore_break(struct repository *, int);
 void diffcore_rename(struct diff_options *);
 void diffcore_rename_extended(struct diff_options *options,
+			      struct strset *relevant_sources,
 			      struct strset *dirs_removed,
 			      struct strmap *dir_rename_count);
 void diffcore_merge_broken(void);
diff --git a/merge-ort.c b/merge-ort.c
index 467404cc0a35..aba0b9fa54c3 100644
--- a/merge-ort.c
+++ b/merge-ort.c
@@ -2029,6 +2029,7 @@ static void detect_regular_renames(struct merge_options *opt,
 	diff_queued_diff = renames->pairs[side_index];
 	trace2_region_enter("diff", "diffcore_rename", opt->repo);
 	diffcore_rename_extended(&diff_opts,
+				 NULL,
 				 &renames->dirs_removed[side_index],
 				 &renames->dir_rename_count[side_index]);
 	trace2_region_leave("diff", "diffcore_rename", opt->repo);

-- 
gitgitgadget

Derrick Stolee· Mar 9, 2021, 22:21 UTC · re: Elijah Newren via GitGitGadget · lore

Re: [PATCH v2 1/8] diffcore-rename: enable filtering possible rename sources

On 3/8/2021 7:09 PM, Elijah Newren via GitGitGadget wrote:> @@ -1127,9 +1137,10 @@ void diffcore_rename_extended(struct diff_options *options,

Show 9 quoted lines

>  		/*
>  		 * Cull sources:
>  		 *   - remove ones corresponding to exact renames
> +		 *   - remove ones not found in relevant_sources
>  		 */
>  		trace2_region_enter("diff", "cull after exact", options->repo);
> -		remove_unneeded_paths_from_src(want_copies);
> +		remove_unneeded_paths_from_src(want_copies, relevant_sources);
>  		trace2_region_leave("diff", "cull after exact", options->repo);

In this case, we are checking for copies. Perhaps there is a reason why we want to include relevant_sources in that case, so I'll look for it later.

Show 21 quoted lines

>  	} else {
>  		/* Determine minimum score to match basenames */
> @@ -1148,7 +1159,7 @@ void diffcore_rename_extended(struct diff_options *options,
>  		 *   - remove ones involved in renames (found via exact match)
>  		 */
>  		trace2_region_enter("diff", "cull after exact", options->repo);
> -		remove_unneeded_paths_from_src(want_copies);
> +		remove_unneeded_paths_from_src(want_copies, NULL);
>  		trace2_region_leave("diff", "cull after exact", options->repo);
>  
>  		/* Preparation for basename-driven matching. */
> @@ -1167,9 +1178,10 @@ void diffcore_rename_extended(struct diff_options *options,
>  		/*
>  		 * Cull sources, again:
>  		 *   - remove ones involved in renames (found via basenames)
> +		 *   - remove ones not found in relevant_sources
>  		 */
>  		trace2_region_enter("diff", "cull basename", options->repo);
> -		remove_unneeded_paths_from_src(want_copies);
> +		remove_unneeded_paths_from_src(want_copies, relevant_sources);
>  		trace2_region_leave("diff", "cull basename", options->repo);

This seems backwards from your cover letter. You are using the exact renames _and_ basename matches to remove the unneeded paths. Why are we not stripping out the relevant_sources in the call further up, before we call find_basename_matches()?

Thanks, -Stolee

Elijah Newren· Mar 9, 2021, 22:40 UTC · re: Derrick Stolee · lore

Re: [PATCH v2 1/8] diffcore-rename: enable filtering possible rename sources

On Tue, Mar 9, 2021 at 2:21 PM Derrick Stolee <stolee@gmail.com> wrote:

Show 15 quoted lines

>
> On 3/8/2021 7:09 PM, Elijah Newren via GitGitGadget wrote:> @@ -1127,9 +1137,10 @@ void diffcore_rename_extended(struct diff_options *options,
> >               /*
> >                * Cull sources:
> >                *   - remove ones corresponding to exact renames
> > +              *   - remove ones not found in relevant_sources
> >                */
> >               trace2_region_enter("diff", "cull after exact", options->repo);
> > -             remove_unneeded_paths_from_src(want_copies);
> > +             remove_unneeded_paths_from_src(want_copies, relevant_sources);
> >               trace2_region_leave("diff", "cull after exact", options->repo);
>
> In this case, we are checking for copies. Perhaps there is a reason
> why we want to include relevant_sources in that case, so I'll look
> for it later.

There is no current caller making use of this. I could have just marked the two options as incompatible and passed NULL here for relevant sources, but...I didn't see a compelling reason to. If some caller wanted copy detection and were only interested in copies from a subset of sources, they could take advantage of relevant_sources in the same way to limit to those paths that are relevant. I guess it comes down to whether you view this as designing the code for future theoretical cases, or explicitly taking steps to limit future possibilities. I don't have a strong opinion here, but tried to enable other future uses since diffcore-rename.c is used by many other callers too.

Show 26 quoted lines

> >       } else {
> >               /* Determine minimum score to match basenames */
> > @@ -1148,7 +1159,7 @@ void diffcore_rename_extended(struct diff_options *options,
> >                *   - remove ones involved in renames (found via exact match)
> >                */
> >               trace2_region_enter("diff", "cull after exact", options->repo);
> > -             remove_unneeded_paths_from_src(want_copies);
> > +             remove_unneeded_paths_from_src(want_copies, NULL);
> >               trace2_region_leave("diff", "cull after exact", options->repo);
> >
> >               /* Preparation for basename-driven matching. */
> > @@ -1167,9 +1178,10 @@ void diffcore_rename_extended(struct diff_options *options,
> >               /*
> >                * Cull sources, again:
> >                *   - remove ones involved in renames (found via basenames)
> > +              *   - remove ones not found in relevant_sources
> >                */
> >               trace2_region_enter("diff", "cull basename", options->repo);
> > -             remove_unneeded_paths_from_src(want_copies);
> > +             remove_unneeded_paths_from_src(want_copies, relevant_sources);
> >               trace2_region_leave("diff", "cull basename", options->repo);
>
> This seems backwards from your cover letter. You are using the exact renames
> _and_ basename matches to remove the unneeded paths. Why are we not stripping
> out the relevant_sources in the call further up, before we call
> find_basename_matches()?

Yeah, good flag. I should add a comment to the commit message about how these are still needed in initialize_dir_rename_info() for basename-guided directory rename detection...and will also play a role in some of the special cases where renames are needed for more than three-way content merges. And add a comment about how by the end of the series, relevant_sources will be passed to find_basename_matches() so that it can skip over those paths.

Derrick Stolee· Mar 9, 2021, 22:45 UTC · re: Elijah Newren · lore

Re: [PATCH v2 1/8] diffcore-rename: enable filtering possible rename sources

On 3/9/2021 5:40 PM, Elijah Newren wrote:

Show 26 quoted lines

> On Tue, Mar 9, 2021 at 2:21 PM Derrick Stolee <stolee@gmail.com> wrote:
>>
>> On 3/8/2021 7:09 PM, Elijah Newren via GitGitGadget wrote:
>>> @@ -1167,9 +1178,10 @@ void diffcore_rename_extended(struct diff_options *options,
>>>               /*
>>>                * Cull sources, again:
>>>                *   - remove ones involved in renames (found via basenames)
>>> +              *   - remove ones not found in relevant_sources
>>>                */
>>>               trace2_region_enter("diff", "cull basename", options->repo);
>>> -             remove_unneeded_paths_from_src(want_copies);
>>> +             remove_unneeded_paths_from_src(want_copies, relevant_sources);
>>>               trace2_region_leave("diff", "cull basename", options->repo);
>>
>> This seems backwards from your cover letter. You are using the exact renames
>> _and_ basename matches to remove the unneeded paths. Why are we not stripping
>> out the relevant_sources in the call further up, before we call
>> find_basename_matches()?
> 
> Yeah, good flag.  I should add a comment to the commit message about
> how these are still needed in initialize_dir_rename_info() for
> basename-guided directory rename detection...and will also play a role
> in some of the special cases where renames are needed for more than
> three-way content merges.  And add a comment about how by the end of
> the series, relevant_sources will be passed to find_basename_matches()
> so that it can skip over those paths.

 
Ah, so by the end, find_basename_matches() will be coupled to the
relevant_sources set directory instead of relying on the culling
happening earlier? Interesting. It seems to me like it would be
better to have them be less coupled by relying on the culling
before calling find_basename_matches(), but I'll keep reading to
see your good reason for not doing that.

Thanks, -Stolee

Elijah Newren via GitGitGadget· Mar 9, 2021, 00:09 UTC · re: Elijah Newren via GitGitGadget · lore

[PATCH v2 6/8] merge-ort: use relevant_sources to filter possible rename sources

From: Elijah Newren <newren@gmail.com>

For the testcases mentioned in commit 557ac0350d ("merge-ort: begin performance work; instrument with trace2_region_* calls", 2020-10-28), this change improves the performance as follows:

                            Before                  After
    no-renames:       12.596 s ±  0.061 s     6.003 s ±  0.048 s
    mega-renames:    130.465 s ±  0.259 s   114.009 s ±  0.236 s
    just-one-mega:     3.958 s ±  0.010 s     3.489 s ±  0.017 s

Signed-off-by: Elijah Newren <newren@gmail.com>
---
 merge-ort.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Show changes to merge-ort.c +1 −1

diff --git a/merge-ort.c b/merge-ort.c
index 27acaa7380be..66892c63cee2 100644
--- a/merge-ort.c
+++ b/merge-ort.c
@@ -2209,7 +2209,7 @@ static void detect_regular_renames(struct merge_options *opt,
 	diff_queued_diff = renames->pairs[side_index];
 	trace2_region_enter("diff", "diffcore_rename", opt->repo);
 	diffcore_rename_extended(&diff_opts,
-				 NULL,
+				 &renames->relevant_sources[side_index],
 				 &renames->dirs_removed[side_index],
 				 &renames->dir_rename_count[side_index]);
 	trace2_region_leave("diff", "diffcore_rename", opt->repo);

-- 
gitgitgadget

Elijah Newren via GitGitGadget· Mar 9, 2021, 00:09 UTC · re: Elijah Newren via GitGitGadget · lore

[PATCH v2 3/8] merge-ort: add data structures for an alternate tree traversal

From: Elijah Newren <newren@gmail.com>

Signed-off-by: Elijah Newren <newren@gmail.com>
---
 merge-ort.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

Show changes to merge-ort.c +26 −0

diff --git a/merge-ort.c b/merge-ort.c
index 83aa4c08121f..d49cfa8b030b 100644
--- a/merge-ort.c
+++ b/merge-ort.c
@@ -51,6 +51,12 @@ enum merge_side {
 	MERGE_SIDE2 = 2
 };
 
+struct traversal_callback_data {
+	unsigned long mask;
+	unsigned long dirmask;
+	struct name_entry names[3];
+};
+
 struct rename_info {
 	/*
 	 * All variables that are arrays of size 3 correspond to data tracked
@@ -102,6 +108,22 @@ struct rename_info {
 	 */
 	struct strset relevant_sources[3];
 
+	/*
+	 * callback_data_*: supporting data structures for alternate traversal
+	 *
+	 * We sometimes need to be able to traverse through all the files
+	 * in a given tree before all immediate subdirectories within that
+	 * tree.  Since traverse_trees() doesn't do that naturally, we have
+	 * a traverse_trees_wrapper() that stores any immediate
+	 * subdirectories while traversing files, then traverses the
+	 * immediate subdirectories later.  These callback_data* variables
+	 * store the information for the subdirectories so that we can do
+	 * that traversal order.
+	 */
+	struct traversal_callback_data *callback_data;
+	int callback_data_nr, callback_data_alloc;
+	char *callback_data_traverse_path;
+
 	/*
 	 * needed_limit: value needed for inexact rename detection to run
 	 *
@@ -396,6 +418,10 @@ static void clear_or_reinit_internal_opts(struct merge_options_internal *opti,
 		}
 		strmap_clear(&opti->output, 0);
 	}
+
+	/* Clean out callback_data as well. */
+	FREE_AND_NULL(renames->callback_data);
+	renames->callback_data_nr = renames->callback_data_alloc = 0;
 }
 
 static int err(struct merge_options *opt, const char *err, ...)

-- 
gitgitgadget

Elijah Newren via GitGitGadget· Mar 9, 2021, 00:09 UTC · re: Elijah Newren via GitGitGadget · lore

[PATCH v2 4/8] merge-ort: introduce wrappers for alternate tree traversal

From: Elijah Newren <newren@gmail.com>

Signed-off-by: Elijah Newren <newren@gmail.com>
---
 merge-ort.c | 72 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 72 insertions(+)

Show changes to merge-ort.c +72 −0

diff --git a/merge-ort.c b/merge-ort.c
index d49cfa8b030b..bd2b93a31141 100644
--- a/merge-ort.c
+++ b/merge-ort.c
@@ -512,6 +512,78 @@ static char *unique_path(struct strmap *existing_paths,
 
 /*** Function Grouping: functions related to collect_merge_info() ***/
 
+static int traverse_trees_wrapper_callback(int n,
+					   unsigned long mask,
+					   unsigned long dirmask,
+					   struct name_entry *names,
+					   struct traverse_info *info)
+{
+	struct merge_options *opt = info->data;
+	struct rename_info *renames = &opt->priv->renames;
+
+	assert(n==3);
+
+	if (!renames->callback_data_traverse_path)
+		renames->callback_data_traverse_path = xstrdup(info->traverse_path);
+
+	ALLOC_GROW(renames->callback_data, renames->callback_data_nr + 1,
+		   renames->callback_data_alloc);
+	renames->callback_data[renames->callback_data_nr].mask = mask;
+	renames->callback_data[renames->callback_data_nr].dirmask = dirmask;
+	COPY_ARRAY(renames->callback_data[renames->callback_data_nr].names,
+		   names, 3);
+	renames->callback_data_nr++;
+
+	return mask;
+}
+
+/*
+ * Much like traverse_trees(), BUT:
+ *   - read all the tree entries FIRST, saving them
+ *   - note that the above step provides an opportunity to compute necessary
+ *     additional details before the "real" traversal
+ *   - loop through the saved entries and call the original callback on them
+ */
+MAYBE_UNUSED
+static int traverse_trees_wrapper(struct index_state *istate,
+				  int n,
+				  struct tree_desc *t,
+				  struct traverse_info *info)
+{
+	int ret, i, old_offset;
+	traverse_callback_t old_fn;
+	char *old_callback_data_traverse_path;
+	struct merge_options *opt = info->data;
+	struct rename_info *renames = &opt->priv->renames;
+
+	old_callback_data_traverse_path = renames->callback_data_traverse_path;
+	old_fn = info->fn;
+	old_offset = renames->callback_data_nr;
+
+	renames->callback_data_traverse_path = NULL;
+	info->fn = traverse_trees_wrapper_callback;
+	ret = traverse_trees(istate, n, t, info);
+	if (ret < 0)
+		return ret;
+
+	info->traverse_path = renames->callback_data_traverse_path;
+	info->fn = old_fn;
+	for (i = old_offset; i < renames->callback_data_nr; ++i) {
+		info->fn(n,
+			 renames->callback_data[i].mask,
+			 renames->callback_data[i].dirmask,
+			 renames->callback_data[i].names,
+			 info);
+
+	}
+
+	renames->callback_data_nr = old_offset;
+	free(renames->callback_data_traverse_path);
+	renames->callback_data_traverse_path = old_callback_data_traverse_path;
+	info->traverse_path = NULL;
+	return 0;
+}
+
 static void setup_path_info(struct merge_options *opt,
 			    struct string_list_item *result,
 			    const char *current_dir_name,

-- 
gitgitgadget

Derrick Stolee· Mar 9, 2021, 23:06 UTC · re: Elijah Newren via GitGitGadget · lore

Re: [PATCH v2 4/8] merge-ort: introduce wrappers for alternate tree traversal

On 3/8/2021 7:09 PM, Elijah Newren via GitGitGadget wrote:

Show 17 quoted lines

> From: Elijah Newren <newren@gmail.com>
> 
> Add traverse_trees_wrapper() and traverse_trees_wrapper_callback()
> functions.  The former runs traverse_trees() with info->fn set to
> traverse_trees_wrapper_callback, in order to simply save all the entries
> without processing or recursing into any of them.  This step allows
> extra computation to be done (e.g. checking some condition across all
> files) that can be used later.  Then, after that is completed, it
> iterates over all the saved entries and calls the original info->fn
> callback with the saved data.
> 
> Currently, this does nothing more than marginally slowing down the tree
> traversal since we do not take advantage of the opportunity to compute
> anything special in traverse_trees_wrapper_callback(), and thus the real
> callback will be called identically as it would have been without this
> extra wrapper.  However, a subsequent commit will add some special
> computation of some values that the real callback will be able to use.

I'm glad that you use the normal callback in the appropriate case.

It took me a couple reads to understand this last sentence, but I think I'm with you now.

Show 9 quoted lines

> +	info->traverse_path = renames->callback_data_traverse_path;
> +	info->fn = old_fn;
> +	for (i = old_offset; i < renames->callback_data_nr; ++i) {
> +		info->fn(n,
> +			 renames->callback_data[i].mask,
> +			 renames->callback_data[i].dirmask,
> +			 renames->callback_data[i].names,
> +			 info);
> +

nit: extraneous newline.

Thanks, -Stolee

Elijah Newren via GitGitGadget· Mar 9, 2021, 00:09 UTC · re: Elijah Newren via GitGitGadget · lore

[PATCH v2 5/8] merge-ort: precompute whether directory rename detection is needed

From: Elijah Newren <newren@gmail.com>

  * If the other side does not add any new files under the old
    directory, we do not need to detect any renames for that directory.

Similarly, directory rename detection had an important requirement:

  * If a directory still exists on one side of history, it has not been
    renamed on that side of history.  (See section 4 of t6423 or
    Documentation/technical/directory-rename-detection.txt for more
    details).

Using these two bits of information, we note that directory rename
detection is only needed in cases where (1) directories exist in the
merge base and on one side of history (i.e. dirmask == 3 or dirmask ==
5), and (2) where there is some new file added to that directory on the
side where it still exists (thus where the file has filemask == 2 or
filemask == 4, respectively).  This has to be done in two steps, because
we have the dirmask when we are first considering the directory, and
won't get the filemasks for the files within it until we recurse into
that directory.  So, we save
  dir_rename_mask = dirmask - 1
when we hit a directory that is missing on one side, and then later look
for cases of
  filemask == dir_rename_mask

The combination of all the above mean that we introduce a variable
named dir_rename_mask (couldn't think of a better name) which has one
of the following values as we traverse into a directory:
   * 0x00: directory rename detection not needed
   * 0x02 or 0x04: directory rename detection only needed if files added
   * 0x07: directory rename detection definitely needed

We then pass this value through to add_pairs() so that it can mark location_relevant as true only when dir_rename_mask is 0x07.

Signed-off-by: Elijah Newren <newren@gmail.com>
---
 merge-ort.c | 67 ++++++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 61 insertions(+), 6 deletions(-)

Show changes to merge-ort.c +61 −6

diff --git a/merge-ort.c b/merge-ort.c
index bd2b93a31141..27acaa7380be 100644
--- a/merge-ort.c
+++ b/merge-ort.c
@@ -108,6 +108,14 @@ struct rename_info {
 	 */
 	struct strset relevant_sources[3];
 
+	/*
+	 * dir_rename_mask:
+	 *   0: optimization removing unmodified potential rename source okay
+	 *   2 or 4: optimization okay, but must check for files added to dir
+	 *   7: optimization forbidden; need rename source in case of dir rename
+	 */
+	unsigned dir_rename_mask:3;
+
 	/*
 	 * callback_data_*: supporting data structures for alternate traversal
 	 *
@@ -419,6 +427,8 @@ static void clear_or_reinit_internal_opts(struct merge_options_internal *opti,
 		strmap_clear(&opti->output, 0);
 	}
 
+	renames->dir_rename_mask = 0;
+
 	/* Clean out callback_data as well. */
 	FREE_AND_NULL(renames->callback_data);
 	renames->callback_data_nr = renames->callback_data_alloc = 0;
@@ -520,12 +530,16 @@ static int traverse_trees_wrapper_callback(int n,
 {
 	struct merge_options *opt = info->data;
 	struct rename_info *renames = &opt->priv->renames;
+	unsigned filemask = mask & ~dirmask;
 
 	assert(n==3);
 
 	if (!renames->callback_data_traverse_path)
 		renames->callback_data_traverse_path = xstrdup(info->traverse_path);
 
+	if (filemask && filemask == renames->dir_rename_mask)
+		renames->dir_rename_mask = 0x07;
+
 	ALLOC_GROW(renames->callback_data, renames->callback_data_nr + 1,
 		   renames->callback_data_alloc);
 	renames->callback_data[renames->callback_data_nr].mask = mask;
@@ -544,7 +558,6 @@ static int traverse_trees_wrapper_callback(int n,
  *     additional details before the "real" traversal
  *   - loop through the saved entries and call the original callback on them
  */
-MAYBE_UNUSED
 static int traverse_trees_wrapper(struct index_state *istate,
 				  int n,
 				  struct tree_desc *t,
@@ -556,6 +569,8 @@ static int traverse_trees_wrapper(struct index_state *istate,
 	struct merge_options *opt = info->data;
 	struct rename_info *renames = &opt->priv->renames;
 
+	assert(renames->dir_rename_mask == 2 || renames->dir_rename_mask == 4);
+
 	old_callback_data_traverse_path = renames->callback_data_traverse_path;
 	old_fn = info->fn;
 	old_offset = renames->callback_data_nr;
@@ -648,7 +663,8 @@ static void add_pair(struct merge_options *opt,
 		     const char *pathname,
 		     unsigned side,
 		     unsigned is_add /* if false, is_delete */,
-		     unsigned match_mask)
+		     unsigned match_mask,
+		     unsigned dir_rename_mask)
 {
 	struct diff_filespec *one, *two;
 	struct rename_info *renames = &opt->priv->renames;
@@ -656,7 +672,7 @@ static void add_pair(struct merge_options *opt,
 
 	if (!is_add) {
 		unsigned content_relevant = (match_mask == 0);
-		unsigned location_relevant = 1; /* FIXME: compute this */
+		unsigned location_relevant = (dir_rename_mask == 0x07);
 
 		if (content_relevant || location_relevant)
 			strset_add(&renames->relevant_sources[side], pathname);
@@ -680,6 +696,36 @@ static void collect_rename_info(struct merge_options *opt,
 	struct rename_info *renames = &opt->priv->renames;
 	unsigned side;
 
+	/*
+	 * Update dir_rename_mask (determines ignore-rename-source validity)
+	 *
+	 * dir_rename_mask helps us keep track of when directory rename
+	 * detection may be relevant.  Basically, whenver a directory is
+	 * removed on one side of history, and a file is added to that
+	 * directory on the other side of history, directory rename
+	 * detection is relevant (meaning we have to detect renames for all
+	 * files within that directory to deduce where the directory
+	 * moved).  Also, whenever a directory needs directory rename
+	 * detection, due to the "majority rules" choice for where to move
+	 * it (see t6423 testcase 1f), we also need to detect renames for
+	 * all files within subdirectories of that directory as well.
+	 *
+	 * Here we haven't looked at files within the directory yet, we are
+	 * just looking at the directory itself.  So, if we aren't yet in
+	 * a case where a parent directory needed directory rename detection
+	 * (i.e. dir_rename_mask != 0x07), and if the directory was removed
+	 * on one side of history, record the mask of the other side of
+	 * history in dir_rename_mask.
+	 */
+	if (renames->dir_rename_mask != 0x07 &&
+	    (dirmask == 3 || dirmask == 5)) {
+		/* simple sanity check */
+		assert(renames->dir_rename_mask == 0 ||
+		       renames->dir_rename_mask == (dirmask & ~1));
+		/* update dir_rename_mask; have it record mask of new side */
+		renames->dir_rename_mask = (dirmask & ~1);
+	}
+
 	/* Update dirs_removed, as needed */
 	if (dirmask == 1 || dirmask == 3 || dirmask == 5) {
 		/* absent_mask = 0x07 - dirmask; sides = absent_mask/2 */
@@ -699,12 +745,14 @@ static void collect_rename_info(struct merge_options *opt,
 		/* Check for deletion on side */
 		if ((filemask & 1) && !(filemask & side_mask))
 			add_pair(opt, names, fullname, side, 0 /* delete */,
-				 match_mask & filemask);
+				 match_mask & filemask,
+				 renames->dir_rename_mask);
 
 		/* Check for addition on side */
 		if (!(filemask & 1) && (filemask & side_mask))
 			add_pair(opt, names, fullname, side, 1 /* add */,
-				 match_mask & filemask);
+				 match_mask & filemask,
+				 renames->dir_rename_mask);
 	}
 }
 
@@ -722,12 +770,14 @@ static int collect_merge_info_callback(int n,
 	 */
 	struct merge_options *opt = info->data;
 	struct merge_options_internal *opti = opt->priv;
+	struct rename_info *renames = &opt->priv->renames;
 	struct string_list_item pi;  /* Path Info */
 	struct conflict_info *ci; /* typed alias to pi.util (which is void*) */
 	struct name_entry *p;
 	size_t len;
 	char *fullpath;
 	const char *dirname = opti->current_dir_name;
+	unsigned prev_dir_rename_mask = renames->dir_rename_mask;
 	unsigned filemask = mask & ~dirmask;
 	unsigned match_mask = 0; /* will be updated below */
 	unsigned mbase_null = !(mask & 1);
@@ -868,8 +918,13 @@ static int collect_merge_info_callback(int n,
 
 		original_dir_name = opti->current_dir_name;
 		opti->current_dir_name = pi.string;
-		ret = traverse_trees(NULL, 3, t, &newinfo);
+		if (renames->dir_rename_mask == 0 ||
+		    renames->dir_rename_mask == 0x07)
+			ret = traverse_trees(NULL, 3, t, &newinfo);
+		else
+			ret = traverse_trees_wrapper(NULL, 3, t, &newinfo);
 		opti->current_dir_name = original_dir_name;
+		renames->dir_rename_mask = prev_dir_rename_mask;
 
 		for (i = MERGE_BASE; i <= MERGE_SIDE2; i++)
 			free(buf[i]);

-- 
gitgitgadget

Elijah Newren via GitGitGadget· Mar 9, 2021, 00:09 UTC · re: Elijah Newren via GitGitGadget · lore

[PATCH v2 8/8] diffcore-rename: avoid doing basename comparisons for irrelevant sources

From: Elijah Newren <newren@gmail.com>

For the testcases mentioned in commit 557ac0350d ("merge-ort: begin performance work; instrument with trace2_region_* calls", 2020-10-28), this change improves the performance as follows:

                            Before                  After
    no-renames:        5.708 s ±  0.111 s     5.680 s ±  0.096 s
    mega-renames:    102.171 s ±  0.440 s    13.812 s ±  0.162 s
    just-one-mega:     3.471 s ±  0.015 s   506.0  ms ±  3.9  ms

Signed-off-by: Elijah Newren <newren@gmail.com>
---
 diffcore-rename.c | 37 +++++++++++++++++++++++++++++++++----
 1 file changed, 33 insertions(+), 4 deletions(-)

Show changes to diffcore-rename.c +33 −4

diff --git a/diffcore-rename.c b/diffcore-rename.c
index 7f6115fd9018..e8508541be14 100644
--- a/diffcore-rename.c
+++ b/diffcore-rename.c
@@ -527,6 +527,7 @@ static void update_dir_rename_counts(struct dir_rename_info *info,
 }
 
 static void initialize_dir_rename_info(struct dir_rename_info *info,
+				       struct strset *relevant_sources,
 				       struct strset *dirs_removed,
 				       struct strmap *dir_rename_count)
 {
@@ -534,7 +535,7 @@ static void initialize_dir_rename_info(struct dir_rename_info *info,
 	struct strmap_entry *entry;
 	int i;
 
-	if (!dirs_removed) {
+	if (!dirs_removed && !relevant_sources) {
 		info->setup = 0;
 		return;
 	}
@@ -549,7 +550,20 @@ static void initialize_dir_rename_info(struct dir_rename_info *info,
 	strmap_init_with_options(&info->dir_rename_guess, NULL, 0);
 
 	/* Setup info->relevant_source_dirs */
-	info->relevant_source_dirs = dirs_removed;
+	info->relevant_source_dirs = NULL;
+	if (dirs_removed || !relevant_sources) {
+		info->relevant_source_dirs = dirs_removed; /* might be NULL */
+	} else {
+		info->relevant_source_dirs = xmalloc(sizeof(struct strintmap));
+		strset_init(info->relevant_source_dirs);
+		strset_for_each_entry(relevant_sources, &iter, entry) {
+			char *dirname = get_dirname(entry->key);
+			if (!dirs_removed ||
+			    strset_contains(dirs_removed, dirname))
+				strset_add(info->relevant_source_dirs, dirname);
+			free(dirname);
+		}
+	}
 
 	/*
 	 * Loop setting up both info->idx_map, and doing setup of
@@ -627,6 +641,13 @@ static void cleanup_dir_rename_info(struct dir_rename_info *info,
 	/* dir_rename_guess */
 	strmap_clear(&info->dir_rename_guess, 1);
 
+	/* relevant_source_dirs */
+	if (info->relevant_source_dirs &&
+	    info->relevant_source_dirs != dirs_removed) {
+		strset_clear(info->relevant_source_dirs);
+		FREE_AND_NULL(info->relevant_source_dirs);
+	}
+
 	/* dir_rename_count */
 	if (!keep_dir_rename_count) {
 		partial_clear_dir_rename_count(info->dir_rename_count);
@@ -749,6 +770,7 @@ static int idx_possible_rename(char *filename, struct dir_rename_info *info)
 static int find_basename_matches(struct diff_options *options,
 				 int minimum_score,
 				 struct dir_rename_info *info,
+				 struct strset *relevant_sources,
 				 struct strset *dirs_removed)
 {
 	/*
@@ -839,6 +861,11 @@ static int find_basename_matches(struct diff_options *options,
 		intptr_t src_index;
 		intptr_t dst_index;
 
+		/* Skip irrelevant sources */
+		if (relevant_sources &&
+		    !strset_contains(relevant_sources, filename))
+			continue;
+
 		/*
 		 * If the basename is unique among remaining sources, then
 		 * src_index will equal 'i' and we can attempt to match it
@@ -1164,7 +1191,7 @@ void diffcore_rename_extended(struct diff_options *options,
 
 		/* Preparation for basename-driven matching. */
 		trace2_region_enter("diff", "dir rename setup", options->repo);
-		initialize_dir_rename_info(&info,
+		initialize_dir_rename_info(&info, relevant_sources,
 					   dirs_removed, dir_rename_count);
 		trace2_region_leave("diff", "dir rename setup", options->repo);
 
@@ -1172,7 +1199,9 @@ void diffcore_rename_extended(struct diff_options *options,
 		trace2_region_enter("diff", "basename matches", options->repo);
 		rename_count += find_basename_matches(options,
 						      min_basename_score,
-						      &info, dirs_removed);
+						      &info,
+						      relevant_sources,
+						      dirs_removed);
 		trace2_region_leave("diff", "basename matches", options->repo);
 
 		/*

-- 
gitgitgadget

Elijah Newren via GitGitGadget· Mar 9, 2021, 00:09 UTC · re: Elijah Newren via GitGitGadget · lore

[PATCH v2 7/8] merge-ort: skip rename detection entirely if possible

From: Elijah Newren <newren@gmail.com>

diffcore_rename_extended() will do a bunch of setup, then check for
exact renames, then abort before inexact rename detection if there are
no more sources or destinations that need to be matched.  It will
sometimes be the case, however, that either
  * we start with neither any sources or destinations
  * we start with no *relevant* sources
In the first of these two cases, the setup and exact rename detection
will be very cheap since there are 0 files to operate on.  In the second
case, it is quite possible to have thousands of files with none of the
source ones being relevant.  Avoid calling diffcore_rename_extended() or
even some of the setup before diffcore_rename_extended() when we can
determine that rename detection is unnecessary.

For the testcases mentioned in commit 557ac0350d ("merge-ort: begin performance work; instrument with trace2_region_* calls", 2020-10-28), this change improves the performance as follows:

                            Before                  After
    no-renames:        6.003 s ±  0.048 s     5.708 s ±  0.111 s
    mega-renames:    114.009 s ±  0.236 s   102.171 s ±  0.440 s
    just-one-mega:     3.489 s ±  0.017 s     3.471 s ±  0.015 s

Signed-off-by: Elijah Newren <newren@gmail.com>
---
 merge-ort.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)

Show changes to merge-ort.c +45 −0

diff --git a/merge-ort.c b/merge-ort.c
index 66892c63cee2..8602c7b8936f 100644
--- a/merge-ort.c
+++ b/merge-ort.c
@@ -2158,6 +2158,19 @@ static int process_renames(struct merge_options *opt,
 	return clean_merge;
 }
 
+static inline int possible_side_renames(struct rename_info *renames,
+					unsigned side_index)
+{
+	return renames->pairs[side_index].nr > 0 &&
+	       !strset_empty(&renames->relevant_sources[side_index]);
+}
+
+static inline int possible_renames(struct rename_info *renames)
+{
+	return possible_side_renames(renames, 1) ||
+	       possible_side_renames(renames, 2);
+}
+
 static void resolve_diffpair_statuses(struct diff_queue_struct *q)
 {
 	/*
@@ -2194,6 +2207,16 @@ static void detect_regular_renames(struct merge_options *opt,
 	struct diff_options diff_opts;
 	struct rename_info *renames = &opt->priv->renames;
 
+	if (!possible_side_renames(renames, side_index)) {
+		/*
+		 * No rename detection needed for this side, but we still need
+		 * to make sure 'adds' are marked correctly in case the other
+		 * side had directory renames.
+		 */
+		resolve_diffpair_statuses(&renames->pairs[side_index]);
+		return;
+	}
+
 	repo_diff_setup(opt->repo, &diff_opts);
 	diff_opts.flags.recursive = 1;
 	diff_opts.flags.rename_empty = 0;
@@ -2311,6 +2334,8 @@ static int detect_and_process_renames(struct merge_options *opt,
 	int need_dir_renames, s, clean = 1;
 
 	memset(&combined, 0, sizeof(combined));
+	if (!possible_renames(renames))
+		goto cleanup;
 
 	trace2_region_enter("merge", "regular renames", opt->repo);
 	detect_regular_renames(opt, MERGE_SIDE1);
@@ -2345,6 +2370,26 @@ static int detect_and_process_renames(struct merge_options *opt,
 	clean &= process_renames(opt, &combined);
 	trace2_region_leave("merge", "process renames", opt->repo);
 
+	goto simple_cleanup; /* collect_renames() handles some of cleanup */
+
+cleanup:
+	/*
+	 * Free now unneeded filepairs, which would have been handled
+	 * in collect_renames() normally but we're about to skip that
+	 * code...
+	 */
+	for (s = MERGE_SIDE1; s <= MERGE_SIDE2; s++) {
+		struct diff_queue_struct *side_pairs;
+		int i;
+
+		side_pairs = &renames->pairs[s];
+		for (i = 0; i < side_pairs->nr; ++i) {
+			struct diff_filepair *p = side_pairs->queue[i];
+			diff_free_filepair(p);
+		}
+	}
+
+simple_cleanup:
 	/* Free memory for renames->pairs[] and combined */
 	for (s = MERGE_SIDE1; s <= MERGE_SIDE2; s++) {
 		free(renames->pairs[s].queue);

-- 
gitgitgadget

Derrick Stolee· Mar 9, 2021, 22:51 UTC · re: Elijah Newren via GitGitGadget · lore

Re: [PATCH v2 7/8] merge-ort: skip rename detection entirely if possible

On 3/8/2021 7:09 PM, Elijah Newren via GitGitGadget wrote:> +	goto simple_cleanup; /* collect_renames() handles some of cleanup */

Show 7 quoted lines

> +
> +cleanup:
> +	/*
> +	 * Free now unneeded filepairs, which would have been handled
> +	 * in collect_renames() normally but we're about to skip that
> +	 * code...
> +	 */

"but we're about to skip that code"

Haven't you skipped it already, earlier in the above part? This should instead say "but we skipped that code", right?

Thanks, -Stolee

Elijah Newren· Mar 9, 2021, 22:57 UTC · re: Derrick Stolee · lore

Re: [PATCH v2 7/8] merge-ort: skip rename detection entirely if possible

On Tue, Mar 9, 2021 at 2:51 PM Derrick Stolee <stolee@gmail.com> wrote:

Show 14 quoted lines

>
> On 3/8/2021 7:09 PM, Elijah Newren via GitGitGadget wrote:> +   goto simple_cleanup; /* collect_renames() handles some of cleanup */
> > +
> > +cleanup:
> > +     /*
> > +      * Free now unneeded filepairs, which would have been handled
> > +      * in collect_renames() normally but we're about to skip that
> > +      * code...
> > +      */
>
> "but we're about to skip that code"
>
> Haven't you skipped it already, earlier in the above part? This should
> instead say "but we skipped that code", right?

Oh, indeed. I wonder if I moved that comment around and didn't update it. Anyway yes, I'll fix it.

Derrick Stolee· Mar 9, 2021, 22:08 UTC · re: Elijah Newren via GitGitGadget · lore

Re: [PATCH v2 0/8] Optimization batch 9: avoid detecting irrelevant renames

On 3/8/2021 7:09 PM, Elijah Newren via GitGitGadget wrote:> The basic idea here is:

Show 15 quoted lines

> 
> We only need expensive rename detection on the subset of files changed on
> both sides of history (for the most part).
> 
> This is because:
> 
>  1. The primary reason for rename detection in merges is enabling three-way
>     content merges
>  2. The purpose of three-way content merges is reconciling changes when
> 
> both sides of history modified some file 3. If a file was only modified by
> the side that renamed the file, then detecting the rename is irrelevant;
> we'll get the same answer without knowing about the rename. 4. (Well...there
> are rare cases where we need the rename for reasons other than three-way
> content merges. Patch 5 explains those.)

Makes sense. Don't compute information you won't need. I look forward to
trying to figure out the special cases here.

>                      Before Series           After Series
> no-renames:       12.596 s ±  0.061 s     5.680 s ±  0.096 s
> mega-renames:    130.465 s ±  0.259 s    13.812 s ±  0.162 s
> just-one-mega:     3.958 s ±  0.010 s   506.0  ms ±  3.9  ms

These are _very_ impressive numbers for such a "simple" idea.

Show 8 quoted lines

> However, interestingly, if we had ignored the basename-guided rename
> detection optimizations[2][3], then this optimization series would have
> improved the performance as follows:
> 
>                Before Basename Series   After Just This Series
> no-renames:      13.815 s ±  0.062 s      5.728 s ±  0.104 s
> mega-renames:  1799.937 s ±  0.493 s     18.213 s ±  0.139 s
> just-one-mega    51.289 s ±  0.019 s    891.9  ms ±  7.0  ms

And here it is even more impressive. I see that your optimizations are having combined effects but also are doing valuable things on their own.

Show 5 quoted lines

> We get best results by prioritizing them as follows:
> 
>  1. exact rename detection
>  2. skip-because-unnecessary
>  3. basename-guided rename detection

This makes sense to me, since even the basename-guided rename is doing some non-trivial work. It would be good to reduce that effort.

> it means that our remaining optimization potential is
> somewhat limited, and subsequent optimization series will have to fight for
> much smaller gains.

This is a good place to end up. Let the code rest for a bit after we are done here, and maybe we'll find new cases to care about later. We could chase the long tail forever, but these steps are a huge accomplishment!

Getting to reading now.

-Stolee

Derrick Stolee· Mar 10, 2021, 15:08 UTC · re: Elijah Newren via GitGitGadget · lore

Re: [PATCH v2 0/8] Optimization batch 9: avoid detecting irrelevant renames

On 3/8/2021 7:09 PM, Elijah Newren via GitGitGadget wrote:

Show 20 quoted lines

> This series depends textually on ort-perf-batch-8, but semantically it's
> almost completely unrelated and can be reviewed without any familiarity with
> any of the previous patch series.
> 
> There are no changes since v1; it's just a resend just over a week later to
> bump it so it isn't lost.
> 
> === Basic Optimization idea ===
> 
> This series determines paths which meet special cases where detection of
> renames is irrelevant, where the irrelevance is due to the fact that the
> merge machinery will arrive at the same result regardless of whether a
> rename is detected for any of those paths. This series represents
> "Optimization #2" from my Git Merge 2020 talk[1], though this series has
> some improvements on the optimization relative to what I had at that time.
> 
> The basic idea here is:
> 
> We only need expensive rename detection on the subset of files changed on
> both sides of history (for the most part).

I've taken time this morning to re-read some of the patches. I have a grasp on the idea of the optimization and the code looks well presented and correct.

The only issue I have is that there are no additional tests to ensure that these scenarios are being tested and are checked to return the correct results. Naturally, it seems we are not testing the ORT strategy by default, and if I do enable it, that causes test failures still.

I wonder how much we should be merging these optimizations before the full test suite can pass with ORT as the default. Then, we can check to see if small mutations can be caught by the test suite. In particular, everything in this optimization seems to revolve around this condition in add_pair():

		if (content_relevant || location_relevant)
			strset_add(&renames->relevant_sources[side], pathname);

I'd prefer to have test cases that cover all four options for the two boolean values on this operator. Mostly, I'd like to know that if I delete either side of the || operator (or change it to &&) then we would have a test failure.

Thanks, -Stolee

Elijah Newren via GitGitGadget· Mar 11, 2021, 00:38 UTC · re: Elijah Newren via GitGitGadget · lore

[PATCH v3 0/8] Optimization batch 9: avoid detecting irrelevant renames

Changes since v2:

 * Added an extended comment about filtering order to the first patch, to
   address Stolee's question
 * Added a new testcase that will fail if the critical "if (content_relevant
   || location_relevant)" check only checks for one of those two or the
   intersection of those two, as suggested by Stolee
 * Fixed the other minor problems Stolee pointed out in his review (stray
   newline, wording of comment)

Elijah Newren (8):
  diffcore-rename: enable filtering possible rename sources
  merge-ort: precompute subset of sources for which we need rename
    detection
  merge-ort: add data structures for an alternate tree traversal
  merge-ort: introduce wrappers for alternate tree traversal
  merge-ort: precompute whether directory rename detection is needed
  merge-ort: use relevant_sources to filter possible rename sources
  merge-ort: skip rename detection entirely if possible
  diffcore-rename: avoid doing basename comparisons for irrelevant
    sources

 diffcore-rename.c                   |  63 ++++++--
 diffcore.h                          |   1 +
 merge-ort.c                         | 234 +++++++++++++++++++++++++++-
 t/t6423-merge-rename-directories.sh |  71 +++++++++
 4 files changed, 354 insertions(+), 15 deletions(-)

base-commit: 4be565c472088d4144063b736308bf2a57331f45
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-845%2Fnewren%2Fort-perf-batch-9-v3
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-845/newren/ort-perf-batch-9-v3
Pull-Request: https://github.com/gitgitgadget/git/pull/845

Range-diff vs v2:

 1:  dab8e3c6aee5 ! 1:  3b253f5a63ed diffcore-rename: enable filtering possible rename sources
     @@ Commit message
          sources we detect renames for, and have merge-ort pass that set of
          relevant_sources to diffcore_rename_extended().
      
     +    A note about filtering order:
     +
     +    Some may be curious why we don't filter out irrelevant sources at the
     +    same time we filter out exact renames.  While that technically could be
     +    done at this point, there are two reasons to defer it:
     +
     +    First, was to reinforce a lesson that was too easy to forget.  As I
     +    mentioned above, in the past I filtered irrelevant sources out before
     +    exact rename checking, and then discovered that exact renames' ability
     +    to remove both sources and destinations was an important consideration
     +    and thus doing the filtering after exact rename checking would speed
     +    things up.  Then at some point I realized that basename matching could
     +    also remove both sources and destinations, and decided to put irrelevant
     +    source filtering after basename filtering.  That slowed things down a
     +    lot.  But, despite learning about this important ordering, in later
     +    restructuring I forgot and made the same mistake of putting the
     +    filtering after basename guided rename detection again.  So, I have this
     +    series of patches structured to do the irrelevant filtering last to
     +    start to show how much extra it costs, and then add relevant filtering
     +    in to find_basename_matches() to show how much it speeds things up.
     +    Basically, it's a way to reinforce something that apparently was too
     +    easy to forget, and make sure the commit messages record this lesson.
     +
     +    Second, the items in the "relevant_sources" in this patch series will
     +    include all sources that *might be* relevant.  It has to be conservative
     +    and catch anything that might need a rename, but in the patch series
     +    after this one we'll find ways to weed out more of the *might be*
     +    relevant ones.  Unfortunately, merge-ort does not have sufficient
     +    information to weed those ones out, and there isn't enough information
     +    at the time of filtering exact renames out to remove the extra ones
     +    either.  It has to be deferred.  So the deferral is in part to simplify
     +    some later additions.
     +
          Signed-off-by: Elijah Newren <newren@gmail.com>
      
       ## diffcore-rename.c ##
 2:  33c231331744 ! 2:  d8378b3dde6c merge-ort: precompute subset of sources for which we need rename detection
     @@ Commit message
                 found under a different path than in the merge base or on the
                 other side of history.
      
     -    This commit concentrates just on the three-way content merging; it will
     -    punt and mark all sources as needed for directory rename detection, and
     -    leave it to future commits to narrow that down more.
     +    Add a simple testcase showing the two kinds of reasons renames are
     +    relevant; it's a testcase that will only pass if we detect both kinds of
     +    needed renames.
     +
     +    Other than the testcase added above, this commit concentrates just on
     +    the three-way content merging; it will punt and mark all sources as
     +    needed for directory rename detection, and leave it to future commits to
     +    narrow that down more.
      
          The point of three-way content merging is to reconcile changes made on
          *both* sides of history.  What if the file wasn't modified on both
     @@ merge-ort.c: static void merge_start(struct merge_options *opt, struct merge_res
       	}
       
       	/*
     +
     + ## t/t6423-merge-rename-directories.sh ##
     +@@ t/t6423-merge-rename-directories.sh: test_expect_merge_algorithm failure success '12f: Trivial directory resolve, cac
     + 	)
     + '
     + 
     ++# Testcase 12g, Testcase with two kinds of "relevant" renames
     ++#   Commit O: somefile_O, subdir/{a_O,b_O}
     ++#   Commit A: somefile_A, subdir/{a_O,b_O,c_A}
     ++#   Commit B: newfile_B,  newdir/{a_B,b_B}
     ++#   Expected: newfile_{merged}, newdir/{a_B,b_B,c_A}
     ++
     ++test_setup_12g () {
     ++	test_create_repo 12g &&
     ++	(
     ++		cd 12g &&
     ++
     ++		mkdir -p subdir &&
     ++		test_write_lines upon a time there was a >somefile &&
     ++		test_write_lines 1 2 3 4 5 6 7 8 9 10 >subdir/a &&
     ++		test_write_lines one two three four five six >subdir/b &&
     ++		git add . &&
     ++		test_tick &&
     ++		git commit -m "O" &&
     ++
     ++		git branch O &&
     ++		git branch A &&
     ++		git branch B &&
     ++
     ++		git switch A &&
     ++		test_write_lines once upon a time there was a >somefile &&
     ++		> subdir/c &&
     ++		git add somefile subdir/c &&
     ++		test_tick &&
     ++		git commit -m "A" &&
     ++
     ++		git checkout B &&
     ++		git mv somefile newfile &&
     ++		git mv subdir newdir &&
     ++		echo repo >>newfile &&
     ++		test_write_lines 1 2 3 4 5 6 7 8 9 10 11 >newdir/a &&
     ++		test_write_lines one two three four five six seven >newdir/b &&
     ++		git add newfile newdir &&
     ++		test_tick &&
     ++		git commit -m "B"
     ++	)
     ++}
     ++
     ++test_expect_success '12g: Testcase with two kinds of "relevant" renames' '
     ++	test_setup_12g &&
     ++	(
     ++		cd 12g &&
     ++
     ++		git checkout A^0 &&
     ++
     ++		git -c merge.directoryRenames=true merge -s recursive B^0 &&
     ++
     ++		test_write_lines once upon a time there was a repo >expect &&
     ++		test_cmp expect newfile &&
     ++
     ++		git ls-files -s >out &&
     ++		test_line_count = 4 out &&
     ++
     ++		git rev-parse >actual \
     ++			HEAD:newdir/a  HEAD:newdir/b   HEAD:newdir/c &&
     ++		git rev-parse >expect \
     ++			B:newdir/a     B:newdir/b      A:subdir/c &&
     ++		test_cmp expect actual &&
     ++
     ++		test_must_fail git rev-parse HEAD:subdir/a &&
     ++		test_must_fail git rev-parse HEAD:subdir/b &&
     ++		test_must_fail git rev-parse HEAD:subdir/c &&
     ++		test_path_is_missing subdir/ &&
     ++		test_path_is_file newdir/c
     ++	)
     ++'
     ++
     + ###########################################################################
     + # SECTION 13: Checking informational and conflict messages
     + #
 3:  89b43c9f75a0 = 3:  a57cc981608c merge-ort: add data structures for an alternate tree traversal
 4:  6497050c0012 ! 4:  b595245fe902 merge-ort: introduce wrappers for alternate tree traversal
     @@ merge-ort.c: static char *unique_path(struct strmap *existing_paths,
      +			 renames->callback_data[i].dirmask,
      +			 renames->callback_data[i].names,
      +			 info);
     -+
      +	}
      +
      +	renames->callback_data_nr = old_offset;
 5:  608d5a4c6ad7 = 5:  dc146a867b16 merge-ort: precompute whether directory rename detection is needed
 6:  d62fdee45ad3 = 6:  375c9b36861b merge-ort: use relevant_sources to filter possible rename sources
 7:  cd931286f24d ! 7:  80a0c27a74ad merge-ort: skip rename detection entirely if possible
     @@ merge-ort.c: static int detect_and_process_renames(struct merge_options *opt,
      +cleanup:
      +	/*
      +	 * Free now unneeded filepairs, which would have been handled
     -+	 * in collect_renames() normally but we're about to skip that
     -+	 * code...
     ++	 * in collect_renames() normally but we skipped that code.
      +	 */
      +	for (s = MERGE_SIDE1; s <= MERGE_SIDE2; s++) {
      +		struct diff_queue_struct *side_pairs;
 8:  c443ba8abb89 = 8:  98b0c7de5e70 diffcore-rename: avoid doing basename comparisons for irrelevant sources

-- 
gitgitgadget

Elijah Newren via GitGitGadget· Mar 11, 2021, 00:38 UTC · re: Elijah Newren via GitGitGadget · lore

[PATCH v3 1/8] diffcore-rename: enable filtering possible rename sources

From: Elijah Newren <newren@gmail.com>

There are two important pieces to this optimization that may not be obvious at first glance:

  * We do not require callers to just filter the filepairs out
    to remove the non-relevant sources, because exact rename detection
    is fast and when it finds a match it can remove both a source and a
    destination whereas the relevant_sources filter can only remove a
    source.

  * We need to filter out the source pairs in a preliminary pass instead
    of adding a
       strset_contains(relevant_sources, one->path)
    check within the nested matrix loop.  The reason for that is if we
    have 30k renames, doing 30k * 30k = 900M strset_contains() calls
    becomes extraordinarily expensive and defeats the performance gains
    from this change; we only want to do 30k such calls instead.

A note about filtering order:

Some may be curious why we don't filter out irrelevant sources at the same time we filter out exact renames. While that technically could be done at this point, there are two reasons to defer it:

First, was to reinforce a lesson that was too easy to forget. As I mentioned above, in the past I filtered irrelevant sources out before exact rename checking, and then discovered that exact renames' ability to remove both sources and destinations was an important consideration and thus doing the filtering after exact rename checking would speed things up. Then at some point I realized that basename matching could also remove both sources and destinations, and decided to put irrelevant source filtering after basename filtering. That slowed things down a lot. But, despite learning about this important ordering, in later restructuring I forgot and made the same mistake of putting the filtering after basename guided rename detection again. So, I have this series of patches structured to do the irrelevant filtering last to start to show how much extra it costs, and then add relevant filtering in to find_basename_matches() to show how much it speeds things up. Basically, it's a way to reinforce something that apparently was too easy to forget, and make sure the commit messages record this lesson.

Second, the items in the "relevant_sources" in this patch series will include all sources that *might be* relevant. It has to be conservative and catch anything that might need a rename, but in the patch series after this one we'll find ways to weed out more of the *might be* relevant ones. Unfortunately, merge-ort does not have sufficient information to weed those ones out, and there isn't enough information at the time of filtering exact renames out to remove the extra ones either. It has to be deferred. So the deferral is in part to simplify some later additions.

Signed-off-by: Elijah Newren <newren@gmail.com>
---
 diffcore-rename.c | 26 +++++++++++++++++++-------
 diffcore.h        |  1 +
 merge-ort.c       |  1 +
 3 files changed, 21 insertions(+), 7 deletions(-)

Show changes to 3 files +21 −7

diffcore-rename.c, diffcore.h, merge-ort.c

diff --git a/diffcore-rename.c b/diffcore-rename.c
index 1fe902ed2af0..7f6115fd9018 100644
--- a/diffcore-rename.c
+++ b/diffcore-rename.c
@@ -991,11 +991,12 @@ static int find_renames(struct diff_score *mx,
 	return count;
 }
 
-static void remove_unneeded_paths_from_src(int detecting_copies)
+static void remove_unneeded_paths_from_src(int detecting_copies,
+					   struct strset *interesting)
 {
 	int i, new_num_src;
 
-	if (detecting_copies)
+	if (detecting_copies && !interesting)
 		return; /* nothing to remove */
 	if (break_idx)
 		return; /* culling incompatible with break detection */
@@ -1022,12 +1023,18 @@ static void remove_unneeded_paths_from_src(int detecting_copies)
 	 *      from rename_src here.
 	 */
 	for (i = 0, new_num_src = 0; i < rename_src_nr; i++) {
+		struct diff_filespec *one = rename_src[i].p->one;
+
 		/*
 		 * renames are stored in rename_dst, so if a rename has
 		 * already been detected using this source, we can just
 		 * remove the source knowing rename_dst has its info.
 		 */
-		if (rename_src[i].p->one->rename_used)
+		if (!detecting_copies && one->rename_used)
+			continue;
+
+		/* If we don't care about the source path, skip it */
+		if (interesting && !strset_contains(interesting, one->path))
 			continue;
 
 		if (new_num_src < i)
@@ -1040,6 +1047,7 @@ static void remove_unneeded_paths_from_src(int detecting_copies)
 }
 
 void diffcore_rename_extended(struct diff_options *options,
+			      struct strset *relevant_sources,
 			      struct strset *dirs_removed,
 			      struct strmap *dir_rename_count)
 {
@@ -1060,6 +1068,8 @@ void diffcore_rename_extended(struct diff_options *options,
 	want_copies = (detect_rename == DIFF_DETECT_COPY);
 	if (dirs_removed && (break_idx || want_copies))
 		BUG("dirs_removed incompatible with break/copy detection");
+	if (break_idx && relevant_sources)
+		BUG("break detection incompatible with source specification");
 	if (!minimum_score)
 		minimum_score = DEFAULT_RENAME_SCORE;
 
@@ -1127,9 +1137,10 @@ void diffcore_rename_extended(struct diff_options *options,
 		/*
 		 * Cull sources:
 		 *   - remove ones corresponding to exact renames
+		 *   - remove ones not found in relevant_sources
 		 */
 		trace2_region_enter("diff", "cull after exact", options->repo);
-		remove_unneeded_paths_from_src(want_copies);
+		remove_unneeded_paths_from_src(want_copies, relevant_sources);
 		trace2_region_leave("diff", "cull after exact", options->repo);
 	} else {
 		/* Determine minimum score to match basenames */
@@ -1148,7 +1159,7 @@ void diffcore_rename_extended(struct diff_options *options,
 		 *   - remove ones involved in renames (found via exact match)
 		 */
 		trace2_region_enter("diff", "cull after exact", options->repo);
-		remove_unneeded_paths_from_src(want_copies);
+		remove_unneeded_paths_from_src(want_copies, NULL);
 		trace2_region_leave("diff", "cull after exact", options->repo);
 
 		/* Preparation for basename-driven matching. */
@@ -1167,9 +1178,10 @@ void diffcore_rename_extended(struct diff_options *options,
 		/*
 		 * Cull sources, again:
 		 *   - remove ones involved in renames (found via basenames)
+		 *   - remove ones not found in relevant_sources
 		 */
 		trace2_region_enter("diff", "cull basename", options->repo);
-		remove_unneeded_paths_from_src(want_copies);
+		remove_unneeded_paths_from_src(want_copies, relevant_sources);
 		trace2_region_leave("diff", "cull basename", options->repo);
 	}
 
@@ -1342,5 +1354,5 @@ void diffcore_rename_extended(struct diff_options *options,
 
 void diffcore_rename(struct diff_options *options)
 {
-	diffcore_rename_extended(options, NULL, NULL);
+	diffcore_rename_extended(options, NULL, NULL, NULL);
 }
diff --git a/diffcore.h b/diffcore.h
index c6ba64abd198..737c93a6cc79 100644
--- a/diffcore.h
+++ b/diffcore.h
@@ -166,6 +166,7 @@ void partial_clear_dir_rename_count(struct strmap *dir_rename_count);
 void diffcore_break(struct repository *, int);
 void diffcore_rename(struct diff_options *);
 void diffcore_rename_extended(struct diff_options *options,
+			      struct strset *relevant_sources,
 			      struct strset *dirs_removed,
 			      struct strmap *dir_rename_count);
 void diffcore_merge_broken(void);
diff --git a/merge-ort.c b/merge-ort.c
index 467404cc0a35..aba0b9fa54c3 100644
--- a/merge-ort.c
+++ b/merge-ort.c
@@ -2029,6 +2029,7 @@ static void detect_regular_renames(struct merge_options *opt,
 	diff_queued_diff = renames->pairs[side_index];
 	trace2_region_enter("diff", "diffcore_rename", opt->repo);
 	diffcore_rename_extended(&diff_opts,
+				 NULL,
 				 &renames->dirs_removed[side_index],
 				 &renames->dir_rename_count[side_index]);
 	trace2_region_leave("diff", "diffcore_rename", opt->repo);

-- 
gitgitgadget

Elijah Newren via GitGitGadget· Mar 11, 2021, 00:38 UTC · re: Elijah Newren via GitGitGadget · lore

[PATCH v3 3/8] merge-ort: add data structures for an alternate tree traversal

From: Elijah Newren <newren@gmail.com>

Signed-off-by: Elijah Newren <newren@gmail.com>
---
 merge-ort.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

Show changes to merge-ort.c +26 −0

diff --git a/merge-ort.c b/merge-ort.c
index 83aa4c08121f..d49cfa8b030b 100644
--- a/merge-ort.c
+++ b/merge-ort.c
@@ -51,6 +51,12 @@ enum merge_side {
 	MERGE_SIDE2 = 2
 };
 
+struct traversal_callback_data {
+	unsigned long mask;
+	unsigned long dirmask;
+	struct name_entry names[3];
+};
+
 struct rename_info {
 	/*
 	 * All variables that are arrays of size 3 correspond to data tracked
@@ -102,6 +108,22 @@ struct rename_info {
 	 */
 	struct strset relevant_sources[3];
 
+	/*
+	 * callback_data_*: supporting data structures for alternate traversal
+	 *
+	 * We sometimes need to be able to traverse through all the files
+	 * in a given tree before all immediate subdirectories within that
+	 * tree.  Since traverse_trees() doesn't do that naturally, we have
+	 * a traverse_trees_wrapper() that stores any immediate
+	 * subdirectories while traversing files, then traverses the
+	 * immediate subdirectories later.  These callback_data* variables
+	 * store the information for the subdirectories so that we can do
+	 * that traversal order.
+	 */
+	struct traversal_callback_data *callback_data;
+	int callback_data_nr, callback_data_alloc;
+	char *callback_data_traverse_path;
+
 	/*
 	 * needed_limit: value needed for inexact rename detection to run
 	 *
@@ -396,6 +418,10 @@ static void clear_or_reinit_internal_opts(struct merge_options_internal *opti,
 		}
 		strmap_clear(&opti->output, 0);
 	}
+
+	/* Clean out callback_data as well. */
+	FREE_AND_NULL(renames->callback_data);
+	renames->callback_data_nr = renames->callback_data_alloc = 0;
 }
 
 static int err(struct merge_options *opt, const char *err, ...)

-- 
gitgitgadget

Elijah Newren via GitGitGadget· Mar 11, 2021, 00:38 UTC · re: Elijah Newren via GitGitGadget · lore

[PATCH v3 5/8] merge-ort: precompute whether directory rename detection is needed

From: Elijah Newren <newren@gmail.com>

  * If the other side does not add any new files under the old
    directory, we do not need to detect any renames for that directory.

Similarly, directory rename detection had an important requirement:

  * If a directory still exists on one side of history, it has not been
    renamed on that side of history.  (See section 4 of t6423 or
    Documentation/technical/directory-rename-detection.txt for more
    details).

Using these two bits of information, we note that directory rename
detection is only needed in cases where (1) directories exist in the
merge base and on one side of history (i.e. dirmask == 3 or dirmask ==
5), and (2) where there is some new file added to that directory on the
side where it still exists (thus where the file has filemask == 2 or
filemask == 4, respectively).  This has to be done in two steps, because
we have the dirmask when we are first considering the directory, and
won't get the filemasks for the files within it until we recurse into
that directory.  So, we save
  dir_rename_mask = dirmask - 1
when we hit a directory that is missing on one side, and then later look
for cases of
  filemask == dir_rename_mask

The combination of all the above mean that we introduce a variable
named dir_rename_mask (couldn't think of a better name) which has one
of the following values as we traverse into a directory:
   * 0x00: directory rename detection not needed
   * 0x02 or 0x04: directory rename detection only needed if files added
   * 0x07: directory rename detection definitely needed

We then pass this value through to add_pairs() so that it can mark location_relevant as true only when dir_rename_mask is 0x07.

Signed-off-by: Elijah Newren <newren@gmail.com>
---
 merge-ort.c | 67 ++++++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 61 insertions(+), 6 deletions(-)

Show changes to merge-ort.c +61 −6

diff --git a/merge-ort.c b/merge-ort.c
index f8f7d06d481a..5840832cf3ed 100644
--- a/merge-ort.c
+++ b/merge-ort.c
@@ -108,6 +108,14 @@ struct rename_info {
 	 */
 	struct strset relevant_sources[3];
 
+	/*
+	 * dir_rename_mask:
+	 *   0: optimization removing unmodified potential rename source okay
+	 *   2 or 4: optimization okay, but must check for files added to dir
+	 *   7: optimization forbidden; need rename source in case of dir rename
+	 */
+	unsigned dir_rename_mask:3;
+
 	/*
 	 * callback_data_*: supporting data structures for alternate traversal
 	 *
@@ -419,6 +427,8 @@ static void clear_or_reinit_internal_opts(struct merge_options_internal *opti,
 		strmap_clear(&opti->output, 0);
 	}
 
+	renames->dir_rename_mask = 0;
+
 	/* Clean out callback_data as well. */
 	FREE_AND_NULL(renames->callback_data);
 	renames->callback_data_nr = renames->callback_data_alloc = 0;
@@ -520,12 +530,16 @@ static int traverse_trees_wrapper_callback(int n,
 {
 	struct merge_options *opt = info->data;
 	struct rename_info *renames = &opt->priv->renames;
+	unsigned filemask = mask & ~dirmask;
 
 	assert(n==3);
 
 	if (!renames->callback_data_traverse_path)
 		renames->callback_data_traverse_path = xstrdup(info->traverse_path);
 
+	if (filemask && filemask == renames->dir_rename_mask)
+		renames->dir_rename_mask = 0x07;
+
 	ALLOC_GROW(renames->callback_data, renames->callback_data_nr + 1,
 		   renames->callback_data_alloc);
 	renames->callback_data[renames->callback_data_nr].mask = mask;
@@ -544,7 +558,6 @@ static int traverse_trees_wrapper_callback(int n,
  *     additional details before the "real" traversal
  *   - loop through the saved entries and call the original callback on them
  */
-MAYBE_UNUSED
 static int traverse_trees_wrapper(struct index_state *istate,
 				  int n,
 				  struct tree_desc *t,
@@ -556,6 +569,8 @@ static int traverse_trees_wrapper(struct index_state *istate,
 	struct merge_options *opt = info->data;
 	struct rename_info *renames = &opt->priv->renames;
 
+	assert(renames->dir_rename_mask == 2 || renames->dir_rename_mask == 4);
+
 	old_callback_data_traverse_path = renames->callback_data_traverse_path;
 	old_fn = info->fn;
 	old_offset = renames->callback_data_nr;
@@ -647,7 +662,8 @@ static void add_pair(struct merge_options *opt,
 		     const char *pathname,
 		     unsigned side,
 		     unsigned is_add /* if false, is_delete */,
-		     unsigned match_mask)
+		     unsigned match_mask,
+		     unsigned dir_rename_mask)
 {
 	struct diff_filespec *one, *two;
 	struct rename_info *renames = &opt->priv->renames;
@@ -655,7 +671,7 @@ static void add_pair(struct merge_options *opt,
 
 	if (!is_add) {
 		unsigned content_relevant = (match_mask == 0);
-		unsigned location_relevant = 1; /* FIXME: compute this */
+		unsigned location_relevant = (dir_rename_mask == 0x07);
 
 		if (content_relevant || location_relevant)
 			strset_add(&renames->relevant_sources[side], pathname);
@@ -679,6 +695,36 @@ static void collect_rename_info(struct merge_options *opt,
 	struct rename_info *renames = &opt->priv->renames;
 	unsigned side;
 
+	/*
+	 * Update dir_rename_mask (determines ignore-rename-source validity)
+	 *
+	 * dir_rename_mask helps us keep track of when directory rename
+	 * detection may be relevant.  Basically, whenver a directory is
+	 * removed on one side of history, and a file is added to that
+	 * directory on the other side of history, directory rename
+	 * detection is relevant (meaning we have to detect renames for all
+	 * files within that directory to deduce where the directory
+	 * moved).  Also, whenever a directory needs directory rename
+	 * detection, due to the "majority rules" choice for where to move
+	 * it (see t6423 testcase 1f), we also need to detect renames for
+	 * all files within subdirectories of that directory as well.
+	 *
+	 * Here we haven't looked at files within the directory yet, we are
+	 * just looking at the directory itself.  So, if we aren't yet in
+	 * a case where a parent directory needed directory rename detection
+	 * (i.e. dir_rename_mask != 0x07), and if the directory was removed
+	 * on one side of history, record the mask of the other side of
+	 * history in dir_rename_mask.
+	 */
+	if (renames->dir_rename_mask != 0x07 &&
+	    (dirmask == 3 || dirmask == 5)) {
+		/* simple sanity check */
+		assert(renames->dir_rename_mask == 0 ||
+		       renames->dir_rename_mask == (dirmask & ~1));
+		/* update dir_rename_mask; have it record mask of new side */
+		renames->dir_rename_mask = (dirmask & ~1);
+	}
+
 	/* Update dirs_removed, as needed */
 	if (dirmask == 1 || dirmask == 3 || dirmask == 5) {
 		/* absent_mask = 0x07 - dirmask; sides = absent_mask/2 */
@@ -698,12 +744,14 @@ static void collect_rename_info(struct merge_options *opt,
 		/* Check for deletion on side */
 		if ((filemask & 1) && !(filemask & side_mask))
 			add_pair(opt, names, fullname, side, 0 /* delete */,
-				 match_mask & filemask);
+				 match_mask & filemask,
+				 renames->dir_rename_mask);
 
 		/* Check for addition on side */
 		if (!(filemask & 1) && (filemask & side_mask))
 			add_pair(opt, names, fullname, side, 1 /* add */,
-				 match_mask & filemask);
+				 match_mask & filemask,
+				 renames->dir_rename_mask);
 	}
 }
 
@@ -721,12 +769,14 @@ static int collect_merge_info_callback(int n,
 	 */
 	struct merge_options *opt = info->data;
 	struct merge_options_internal *opti = opt->priv;
+	struct rename_info *renames = &opt->priv->renames;
 	struct string_list_item pi;  /* Path Info */
 	struct conflict_info *ci; /* typed alias to pi.util (which is void*) */
 	struct name_entry *p;
 	size_t len;
 	char *fullpath;
 	const char *dirname = opti->current_dir_name;
+	unsigned prev_dir_rename_mask = renames->dir_rename_mask;
 	unsigned filemask = mask & ~dirmask;
 	unsigned match_mask = 0; /* will be updated below */
 	unsigned mbase_null = !(mask & 1);
@@ -867,8 +917,13 @@ static int collect_merge_info_callback(int n,
 
 		original_dir_name = opti->current_dir_name;
 		opti->current_dir_name = pi.string;
-		ret = traverse_trees(NULL, 3, t, &newinfo);
+		if (renames->dir_rename_mask == 0 ||
+		    renames->dir_rename_mask == 0x07)
+			ret = traverse_trees(NULL, 3, t, &newinfo);
+		else
+			ret = traverse_trees_wrapper(NULL, 3, t, &newinfo);
 		opti->current_dir_name = original_dir_name;
+		renames->dir_rename_mask = prev_dir_rename_mask;
 
 		for (i = MERGE_BASE; i <= MERGE_SIDE2; i++)
 			free(buf[i]);

-- 
gitgitgadget

Elijah Newren via GitGitGadget· Mar 11, 2021, 00:38 UTC · re: Elijah Newren via GitGitGadget · lore

[PATCH v3 2/8] merge-ort: precompute subset of sources for which we need rename detection

From: Elijah Newren <newren@gmail.com>

To see why, first note that the merge machinery uses detected renames in two ways:

   * directory rename detection: when one side of history renames a
       directory, and the other side of history adds new files to that
       directory, we want to be able to warn the user about the need to
       chose whether those new files stay in the old directory or move
       to the new one.

   * three-way content merging: in order to do three-way content merging
       of files, we need three different file versions.  If one side of
       history renamed a file, then some of the content for the file is
       found under a different path than in the merge base or on the
       other side of history.

Add a simple testcase showing the two kinds of reasons renames are relevant; it's a testcase that will only pass if we detect both kinds of needed renames.

Other than the testcase added above, this commit concentrates just on the three-way content merging; it will punt and mark all sources as needed for directory rename detection, and leave it to future commits to narrow that down more.

The point of three-way content merging is to reconcile changes made on *both* sides of history. What if the file wasn't modified on both sides? There are two possibilities:

   * If it wasn't modified on the renamed side:
       -> then we get to do exact rename detection, which is cheap.

   * If it wasn't modified on the unrenamed side:
       -> then detection of a rename for that source file is irrelevant

                 old.c     new.c
   MERGE_BASE:   01d01d    000000
   MERGE_SIDE1:  01d01d    000000
   MERGE_SIDE2:  000000    5e1ec7

If the rename *isn't* detected:
   then old.c looks like it was unmodified on one side and deleted on
   the other and should thus be removed.  new.c looks like a new file we
   should keep as-is.

If the rename *is* detected:
   then a three-way content merge is done.  Since the version of the
   file in MERGE_BASE and MERGE_SIDE1 are identical, the three-way merge
   will produce exactly the version of the file whose abbreviated
   object id is 5e1ec7.  It will record that file at the path new.c,
   while removing old.c from the directory.

Use this information to compute whether we need rename detection for each source created in add_pair().

 * bringing consistency to add/add, rename/add, and rename/rename
    conflict types, as done back in the topic merged at commit
    ac193e0e0a ("Merge branch 'en/merge-path-collision'", 2019-01-04),
    and further extended in commits 2a7c16c980 ("t6422, t6426: be more
    flexible for add/add conflicts involving renames", 2020-08-10) and
    e8eb99d4a6 ("t642[23]: be more flexible for add/add conflicts
    involving pair renames", 2020-08-10)

  * making rename/delete more consistent with modify/delete
    as done in commits 1f3c9ba707 ("t6425: be more flexible with
    rename/delete conflict messages", 2020-08-10) and 727c75b23f
    ("t6404, t6423: expect improved rename/delete handling in ort
    backend", 2020-10-26)

Signed-off-by: Elijah Newren <newren@gmail.com>
---
 merge-ort.c                         | 35 ++++++++++++--
 t/t6423-merge-rename-directories.sh | 71 +++++++++++++++++++++++++++++
 2 files changed, 103 insertions(+), 3 deletions(-)

Show changes to 2 files +103 −3

merge-ort.c, t/t6423-merge-rename-directories.sh

diff --git a/merge-ort.c b/merge-ort.c
index aba0b9fa54c3..83aa4c08121f 100644
--- a/merge-ort.c
+++ b/merge-ort.c
@@ -88,6 +88,20 @@ struct rename_info {
 	 */
 	struct strmap dir_renames[3];
 
+	/*
+	 * relevant_sources: deleted paths for which we need rename detection
+	 *
+	 * relevant_sources is a set of deleted paths on each side of
+	 * history for which we need rename detection.  If a path is deleted
+	 * on one side of history, we need to detect if it is part of a
+	 * rename if either
+	 *    * we need to detect renames for an ancestor directory
+	 *    * the file is modified/deleted on the other side of history
+	 * If neither of those are true, we can skip rename detection for
+	 * that path.
+	 */
+	struct strset relevant_sources[3];
+
 	/*
 	 * needed_limit: value needed for inexact rename detection to run
 	 *
@@ -358,6 +372,8 @@ static void clear_or_reinit_internal_opts(struct merge_options_internal *opti,
 			strmap_clear(&renames->dir_rename_count[i], 1);
 
 		strmap_func(&renames->dir_renames[i], 0);
+
+		strset_func(&renames->relevant_sources[i]);
 	}
 
 	if (!reinitialize) {
@@ -533,12 +549,21 @@ static void add_pair(struct merge_options *opt,
 		     struct name_entry *names,
 		     const char *pathname,
 		     unsigned side,
-		     unsigned is_add /* if false, is_delete */)
+		     unsigned is_add /* if false, is_delete */,
+		     unsigned match_mask)
 {
 	struct diff_filespec *one, *two;
 	struct rename_info *renames = &opt->priv->renames;
 	int names_idx = is_add ? side : 0;
 
+	if (!is_add) {
+		unsigned content_relevant = (match_mask == 0);
+		unsigned location_relevant = 1; /* FIXME: compute this */
+
+		if (content_relevant || location_relevant)
+			strset_add(&renames->relevant_sources[side], pathname);
+	}
+
 	one = alloc_filespec(pathname);
 	two = alloc_filespec(pathname);
 	fill_filespec(is_add ? two : one,
@@ -575,11 +600,13 @@ static void collect_rename_info(struct merge_options *opt,
 
 		/* Check for deletion on side */
 		if ((filemask & 1) && !(filemask & side_mask))
-			add_pair(opt, names, fullname, side, 0 /* delete */);
+			add_pair(opt, names, fullname, side, 0 /* delete */,
+				 match_mask & filemask);
 
 		/* Check for addition on side */
 		if (!(filemask & 1) && (filemask & side_mask))
-			add_pair(opt, names, fullname, side, 1 /* add */);
+			add_pair(opt, names, fullname, side, 1 /* add */,
+				 match_mask & filemask);
 	}
 }
 
@@ -3228,6 +3255,8 @@ static void merge_start(struct merge_options *opt, struct merge_result *result)
 					 NULL, 1);
 		strmap_init_with_options(&renames->dir_renames[i],
 					 NULL, 0);
+		strset_init_with_options(&renames->relevant_sources[i],
+					 NULL, 0);
 	}
 
 	/*
diff --git a/t/t6423-merge-rename-directories.sh b/t/t6423-merge-rename-directories.sh
index 4ab133f489ca..4c568050dd27 100755
--- a/t/t6423-merge-rename-directories.sh
+++ b/t/t6423-merge-rename-directories.sh
@@ -4895,6 +4895,77 @@ test_expect_merge_algorithm failure success '12f: Trivial directory resolve, cac
 	)
 '
 
+# Testcase 12g, Testcase with two kinds of "relevant" renames
+#   Commit O: somefile_O, subdir/{a_O,b_O}
+#   Commit A: somefile_A, subdir/{a_O,b_O,c_A}
+#   Commit B: newfile_B,  newdir/{a_B,b_B}
+#   Expected: newfile_{merged}, newdir/{a_B,b_B,c_A}
+
+test_setup_12g () {
+	test_create_repo 12g &&
+	(
+		cd 12g &&
+
+		mkdir -p subdir &&
+		test_write_lines upon a time there was a >somefile &&
+		test_write_lines 1 2 3 4 5 6 7 8 9 10 >subdir/a &&
+		test_write_lines one two three four five six >subdir/b &&
+		git add . &&
+		test_tick &&
+		git commit -m "O" &&
+
+		git branch O &&
+		git branch A &&
+		git branch B &&
+
+		git switch A &&
+		test_write_lines once upon a time there was a >somefile &&
+		> subdir/c &&
+		git add somefile subdir/c &&
+		test_tick &&
+		git commit -m "A" &&
+
+		git checkout B &&
+		git mv somefile newfile &&
+		git mv subdir newdir &&
+		echo repo >>newfile &&
+		test_write_lines 1 2 3 4 5 6 7 8 9 10 11 >newdir/a &&
+		test_write_lines one two three four five six seven >newdir/b &&
+		git add newfile newdir &&
+		test_tick &&
+		git commit -m "B"
+	)
+}
+
+test_expect_success '12g: Testcase with two kinds of "relevant" renames' '
+	test_setup_12g &&
+	(
+		cd 12g &&
+
+		git checkout A^0 &&
+
+		git -c merge.directoryRenames=true merge -s recursive B^0 &&
+
+		test_write_lines once upon a time there was a repo >expect &&
+		test_cmp expect newfile &&
+
+		git ls-files -s >out &&
+		test_line_count = 4 out &&
+
+		git rev-parse >actual \
+			HEAD:newdir/a  HEAD:newdir/b   HEAD:newdir/c &&
+		git rev-parse >expect \
+			B:newdir/a     B:newdir/b      A:subdir/c &&
+		test_cmp expect actual &&
+
+		test_must_fail git rev-parse HEAD:subdir/a &&
+		test_must_fail git rev-parse HEAD:subdir/b &&
+		test_must_fail git rev-parse HEAD:subdir/c &&
+		test_path_is_missing subdir/ &&
+		test_path_is_file newdir/c
+	)
+'
+
 ###########################################################################
 # SECTION 13: Checking informational and conflict messages
 #

-- 
gitgitgadget

Elijah Newren via GitGitGadget· Mar 11, 2021, 00:38 UTC · re: Elijah Newren via GitGitGadget · lore

[PATCH v3 4/8] merge-ort: introduce wrappers for alternate tree traversal

From: Elijah Newren <newren@gmail.com>

Signed-off-by: Elijah Newren <newren@gmail.com>
---
 merge-ort.c | 71 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 71 insertions(+)

Show changes to merge-ort.c +71 −0

diff --git a/merge-ort.c b/merge-ort.c
index d49cfa8b030b..f8f7d06d481a 100644
--- a/merge-ort.c
+++ b/merge-ort.c
@@ -512,6 +512,77 @@ static char *unique_path(struct strmap *existing_paths,
 
 /*** Function Grouping: functions related to collect_merge_info() ***/
 
+static int traverse_trees_wrapper_callback(int n,
+					   unsigned long mask,
+					   unsigned long dirmask,
+					   struct name_entry *names,
+					   struct traverse_info *info)
+{
+	struct merge_options *opt = info->data;
+	struct rename_info *renames = &opt->priv->renames;
+
+	assert(n==3);
+
+	if (!renames->callback_data_traverse_path)
+		renames->callback_data_traverse_path = xstrdup(info->traverse_path);
+
+	ALLOC_GROW(renames->callback_data, renames->callback_data_nr + 1,
+		   renames->callback_data_alloc);
+	renames->callback_data[renames->callback_data_nr].mask = mask;
+	renames->callback_data[renames->callback_data_nr].dirmask = dirmask;
+	COPY_ARRAY(renames->callback_data[renames->callback_data_nr].names,
+		   names, 3);
+	renames->callback_data_nr++;
+
+	return mask;
+}
+
+/*
+ * Much like traverse_trees(), BUT:
+ *   - read all the tree entries FIRST, saving them
+ *   - note that the above step provides an opportunity to compute necessary
+ *     additional details before the "real" traversal
+ *   - loop through the saved entries and call the original callback on them
+ */
+MAYBE_UNUSED
+static int traverse_trees_wrapper(struct index_state *istate,
+				  int n,
+				  struct tree_desc *t,
+				  struct traverse_info *info)
+{
+	int ret, i, old_offset;
+	traverse_callback_t old_fn;
+	char *old_callback_data_traverse_path;
+	struct merge_options *opt = info->data;
+	struct rename_info *renames = &opt->priv->renames;
+
+	old_callback_data_traverse_path = renames->callback_data_traverse_path;
+	old_fn = info->fn;
+	old_offset = renames->callback_data_nr;
+
+	renames->callback_data_traverse_path = NULL;
+	info->fn = traverse_trees_wrapper_callback;
+	ret = traverse_trees(istate, n, t, info);
+	if (ret < 0)
+		return ret;
+
+	info->traverse_path = renames->callback_data_traverse_path;
+	info->fn = old_fn;
+	for (i = old_offset; i < renames->callback_data_nr; ++i) {
+		info->fn(n,
+			 renames->callback_data[i].mask,
+			 renames->callback_data[i].dirmask,
+			 renames->callback_data[i].names,
+			 info);
+	}
+
+	renames->callback_data_nr = old_offset;
+	free(renames->callback_data_traverse_path);
+	renames->callback_data_traverse_path = old_callback_data_traverse_path;
+	info->traverse_path = NULL;
+	return 0;
+}
+
 static void setup_path_info(struct merge_options *opt,
 			    struct string_list_item *result,
 			    const char *current_dir_name,

-- 
gitgitgadget

Elijah Newren via GitGitGadget· Mar 11, 2021, 00:38 UTC · re: Elijah Newren via GitGitGadget · lore

[PATCH v3 8/8] diffcore-rename: avoid doing basename comparisons for irrelevant sources

From: Elijah Newren <newren@gmail.com>

For the testcases mentioned in commit 557ac0350d ("merge-ort: begin performance work; instrument with trace2_region_* calls", 2020-10-28), this change improves the performance as follows:

                            Before                  After
    no-renames:        5.708 s ±  0.111 s     5.680 s ±  0.096 s
    mega-renames:    102.171 s ±  0.440 s    13.812 s ±  0.162 s
    just-one-mega:     3.471 s ±  0.015 s   506.0  ms ±  3.9  ms

Signed-off-by: Elijah Newren <newren@gmail.com>
---
 diffcore-rename.c | 37 +++++++++++++++++++++++++++++++++----
 1 file changed, 33 insertions(+), 4 deletions(-)

Show changes to diffcore-rename.c +33 −4

diff --git a/diffcore-rename.c b/diffcore-rename.c
index 7f6115fd9018..e8508541be14 100644
--- a/diffcore-rename.c
+++ b/diffcore-rename.c
@@ -527,6 +527,7 @@ static void update_dir_rename_counts(struct dir_rename_info *info,
 }
 
 static void initialize_dir_rename_info(struct dir_rename_info *info,
+				       struct strset *relevant_sources,
 				       struct strset *dirs_removed,
 				       struct strmap *dir_rename_count)
 {
@@ -534,7 +535,7 @@ static void initialize_dir_rename_info(struct dir_rename_info *info,
 	struct strmap_entry *entry;
 	int i;
 
-	if (!dirs_removed) {
+	if (!dirs_removed && !relevant_sources) {
 		info->setup = 0;
 		return;
 	}
@@ -549,7 +550,20 @@ static void initialize_dir_rename_info(struct dir_rename_info *info,
 	strmap_init_with_options(&info->dir_rename_guess, NULL, 0);
 
 	/* Setup info->relevant_source_dirs */
-	info->relevant_source_dirs = dirs_removed;
+	info->relevant_source_dirs = NULL;
+	if (dirs_removed || !relevant_sources) {
+		info->relevant_source_dirs = dirs_removed; /* might be NULL */
+	} else {
+		info->relevant_source_dirs = xmalloc(sizeof(struct strintmap));
+		strset_init(info->relevant_source_dirs);
+		strset_for_each_entry(relevant_sources, &iter, entry) {
+			char *dirname = get_dirname(entry->key);
+			if (!dirs_removed ||
+			    strset_contains(dirs_removed, dirname))
+				strset_add(info->relevant_source_dirs, dirname);
+			free(dirname);
+		}
+	}
 
 	/*
 	 * Loop setting up both info->idx_map, and doing setup of
@@ -627,6 +641,13 @@ static void cleanup_dir_rename_info(struct dir_rename_info *info,
 	/* dir_rename_guess */
 	strmap_clear(&info->dir_rename_guess, 1);
 
+	/* relevant_source_dirs */
+	if (info->relevant_source_dirs &&
+	    info->relevant_source_dirs != dirs_removed) {
+		strset_clear(info->relevant_source_dirs);
+		FREE_AND_NULL(info->relevant_source_dirs);
+	}
+
 	/* dir_rename_count */
 	if (!keep_dir_rename_count) {
 		partial_clear_dir_rename_count(info->dir_rename_count);
@@ -749,6 +770,7 @@ static int idx_possible_rename(char *filename, struct dir_rename_info *info)
 static int find_basename_matches(struct diff_options *options,
 				 int minimum_score,
 				 struct dir_rename_info *info,
+				 struct strset *relevant_sources,
 				 struct strset *dirs_removed)
 {
 	/*
@@ -839,6 +861,11 @@ static int find_basename_matches(struct diff_options *options,
 		intptr_t src_index;
 		intptr_t dst_index;
 
+		/* Skip irrelevant sources */
+		if (relevant_sources &&
+		    !strset_contains(relevant_sources, filename))
+			continue;
+
 		/*
 		 * If the basename is unique among remaining sources, then
 		 * src_index will equal 'i' and we can attempt to match it
@@ -1164,7 +1191,7 @@ void diffcore_rename_extended(struct diff_options *options,
 
 		/* Preparation for basename-driven matching. */
 		trace2_region_enter("diff", "dir rename setup", options->repo);
-		initialize_dir_rename_info(&info,
+		initialize_dir_rename_info(&info, relevant_sources,
 					   dirs_removed, dir_rename_count);
 		trace2_region_leave("diff", "dir rename setup", options->repo);
 
@@ -1172,7 +1199,9 @@ void diffcore_rename_extended(struct diff_options *options,
 		trace2_region_enter("diff", "basename matches", options->repo);
 		rename_count += find_basename_matches(options,
 						      min_basename_score,
-						      &info, dirs_removed);
+						      &info,
+						      relevant_sources,
+						      dirs_removed);
 		trace2_region_leave("diff", "basename matches", options->repo);
 
 		/*

-- 
gitgitgadget

Elijah Newren via GitGitGadget· Mar 11, 2021, 00:38 UTC · re: Elijah Newren via GitGitGadget · lore

[PATCH v3 6/8] merge-ort: use relevant_sources to filter possible rename sources

From: Elijah Newren <newren@gmail.com>

For the testcases mentioned in commit 557ac0350d ("merge-ort: begin performance work; instrument with trace2_region_* calls", 2020-10-28), this change improves the performance as follows:

                            Before                  After
    no-renames:       12.596 s ±  0.061 s     6.003 s ±  0.048 s
    mega-renames:    130.465 s ±  0.259 s   114.009 s ±  0.236 s
    just-one-mega:     3.958 s ±  0.010 s     3.489 s ±  0.017 s

Signed-off-by: Elijah Newren <newren@gmail.com>
---
 merge-ort.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Show changes to merge-ort.c +1 −1

diff --git a/merge-ort.c b/merge-ort.c
index 5840832cf3ed..eea14024c657 100644
--- a/merge-ort.c
+++ b/merge-ort.c
@@ -2208,7 +2208,7 @@ static void detect_regular_renames(struct merge_options *opt,
 	diff_queued_diff = renames->pairs[side_index];
 	trace2_region_enter("diff", "diffcore_rename", opt->repo);
 	diffcore_rename_extended(&diff_opts,
-				 NULL,
+				 &renames->relevant_sources[side_index],
 				 &renames->dirs_removed[side_index],
 				 &renames->dir_rename_count[side_index]);
 	trace2_region_leave("diff", "diffcore_rename", opt->repo);

-- 
gitgitgadget

Elijah Newren via GitGitGadget· Mar 11, 2021, 00:38 UTC · re: Elijah Newren via GitGitGadget · lore

[PATCH v3 7/8] merge-ort: skip rename detection entirely if possible

From: Elijah Newren <newren@gmail.com>

diffcore_rename_extended() will do a bunch of setup, then check for
exact renames, then abort before inexact rename detection if there are
no more sources or destinations that need to be matched.  It will
sometimes be the case, however, that either
  * we start with neither any sources or destinations
  * we start with no *relevant* sources
In the first of these two cases, the setup and exact rename detection
will be very cheap since there are 0 files to operate on.  In the second
case, it is quite possible to have thousands of files with none of the
source ones being relevant.  Avoid calling diffcore_rename_extended() or
even some of the setup before diffcore_rename_extended() when we can
determine that rename detection is unnecessary.

For the testcases mentioned in commit 557ac0350d ("merge-ort: begin performance work; instrument with trace2_region_* calls", 2020-10-28), this change improves the performance as follows:

                            Before                  After
    no-renames:        6.003 s ±  0.048 s     5.708 s ±  0.111 s
    mega-renames:    114.009 s ±  0.236 s   102.171 s ±  0.440 s
    just-one-mega:     3.489 s ±  0.017 s     3.471 s ±  0.015 s

Signed-off-by: Elijah Newren <newren@gmail.com>
---
 merge-ort.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)

Show changes to merge-ort.c +44 −0

diff --git a/merge-ort.c b/merge-ort.c
index eea14024c657..bd089cb9a76f 100644
--- a/merge-ort.c
+++ b/merge-ort.c
@@ -2157,6 +2157,19 @@ static int process_renames(struct merge_options *opt,
 	return clean_merge;
 }
 
+static inline int possible_side_renames(struct rename_info *renames,
+					unsigned side_index)
+{
+	return renames->pairs[side_index].nr > 0 &&
+	       !strset_empty(&renames->relevant_sources[side_index]);
+}
+
+static inline int possible_renames(struct rename_info *renames)
+{
+	return possible_side_renames(renames, 1) ||
+	       possible_side_renames(renames, 2);
+}
+
 static void resolve_diffpair_statuses(struct diff_queue_struct *q)
 {
 	/*
@@ -2193,6 +2206,16 @@ static void detect_regular_renames(struct merge_options *opt,
 	struct diff_options diff_opts;
 	struct rename_info *renames = &opt->priv->renames;
 
+	if (!possible_side_renames(renames, side_index)) {
+		/*
+		 * No rename detection needed for this side, but we still need
+		 * to make sure 'adds' are marked correctly in case the other
+		 * side had directory renames.
+		 */
+		resolve_diffpair_statuses(&renames->pairs[side_index]);
+		return;
+	}
+
 	repo_diff_setup(opt->repo, &diff_opts);
 	diff_opts.flags.recursive = 1;
 	diff_opts.flags.rename_empty = 0;
@@ -2310,6 +2333,8 @@ static int detect_and_process_renames(struct merge_options *opt,
 	int need_dir_renames, s, clean = 1;
 
 	memset(&combined, 0, sizeof(combined));
+	if (!possible_renames(renames))
+		goto cleanup;
 
 	trace2_region_enter("merge", "regular renames", opt->repo);
 	detect_regular_renames(opt, MERGE_SIDE1);
@@ -2344,6 +2369,25 @@ static int detect_and_process_renames(struct merge_options *opt,
 	clean &= process_renames(opt, &combined);
 	trace2_region_leave("merge", "process renames", opt->repo);
 
+	goto simple_cleanup; /* collect_renames() handles some of cleanup */
+
+cleanup:
+	/*
+	 * Free now unneeded filepairs, which would have been handled
+	 * in collect_renames() normally but we skipped that code.
+	 */
+	for (s = MERGE_SIDE1; s <= MERGE_SIDE2; s++) {
+		struct diff_queue_struct *side_pairs;
+		int i;
+
+		side_pairs = &renames->pairs[s];
+		for (i = 0; i < side_pairs->nr; ++i) {
+			struct diff_filepair *p = side_pairs->queue[i];
+			diff_free_filepair(p);
+		}
+	}
+
+simple_cleanup:
 	/* Free memory for renames->pairs[] and combined */
 	for (s = MERGE_SIDE1; s <= MERGE_SIDE2; s++) {
 		free(renames->pairs[s].queue);

-- 
gitgitgadget

Derrick Stolee· Mar 15, 2021, 13:57 UTC · re: Elijah Newren via GitGitGadget · lore

Re: [PATCH v3 0/8] Optimization batch 9: avoid detecting irrelevant renames

On 3/10/2021 7:38 PM, Elijah Newren via GitGitGadget wrote:

Show 14 quoted lines

> This series determines paths which meet special cases where detection of
> renames is irrelevant, where the irrelevance is due to the fact that the
> merge machinery will arrive at the same result regardless of whether a
> rename is detected for any of those paths.
> 
> Changes since v2:
> 
>  * Added an extended comment about filtering order to the first patch, to
>    address Stolee's question
>  * Added a new testcase that will fail if the critical "if (content_relevant
>    || location_relevant)" check only checks for one of those two or the
>    intersection of those two, as suggested by Stolee
>  * Fixed the other minor problems Stolee pointed out in his review (stray
>    newline, wording of comment)

Thanks for these updates. This version works for me.

-Stolee

Elijah Newren· Mar 15, 2021, 17:10 UTC · re: Elijah Newren via GitGitGadget · lore

Re: [PATCH v2 0/8] Optimization batch 9: avoid detecting irrelevant renames

On Mon, Mar 8, 2021 at 4:10 PM Elijah Newren via GitGitGadget <gitgitgadget@gmail.com> wrote:

Show 21 quoted lines

>
> This series depends textually on ort-perf-batch-8, but semantically it's
> almost completely unrelated and can be reviewed without any familiarity with
> any of the previous patch series.
>
> There are no changes since v1; it's just a resend just over a week later to
> bump it so it isn't lost.
>
> === Basic Optimization idea ===
>
> This series determines paths which meet special cases where detection of
> renames is irrelevant, where the irrelevance is due to the fact that the
> merge machinery will arrive at the same result regardless of whether a
> rename is detected for any of those paths. This series represents
> "Optimization #2" from my Git Merge 2020 talk[1], though this series has
> some improvements on the optimization relative to what I had at that time.
>
> The basic idea here is:
>
> We only need expensive rename detection on the subset of files changed on
> both sides of history (for the most part).

I know this series was already reviewed and even a subsequent series was reviewed, but I thought I'd insert a bit of history trivia:

I first submitted this optimization in late 2017 as an RFC at https://lore.kernel.org/git/20171110222156.23221-9-newren@gmail.com/. Unfortunately I had only handled the "for the most part" piece, not the other special cases. I knew not handling those other cases caused bugs, but didn't readily find a solution for them at the time. I kept mulling it over periodically despite being switched onto other projects; eventually I weaseled my way into being able to work on it again and with some effort was able to work out the other necessary conditions and audit the code to verify I had all the cases covered. Those "other cases" were much more easily expressed in the context of merge-ort's data structures than merge-recursive's, in part because merge-ort's data structures were picked to help me solve this optimization problem and the various known failing testcases that I wanted to fix.