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Re: [PATCH] process_{tree,blob}: Remove useless xstrdup calls

From
Linus Torvalds <torvalds@linux-foundation.org>
Date
Apr 11, 2009, 00:27 UTC
Message-ID
<alpine.LFD.2.00.0904101714420.4583@localhost.localdomain>
In-Reply-To
<alpine.LFD.2.00.0904101517520.4583@localhost.localdomain>
On Fri, 10 Apr 2009, Linus Torvalds wrote:
> 
> There's another easy 5% or so for the built-in object walker: once we've 
> created the hash from the name, the name isn't interesting any more, and 
> so something trivial like this can help a bit.
Hmm.
Here's a less trivial thing, and slightly more dubious one.

I was looking at that "struct object_array objects", and wondering why we do that. I have honestly totally forgotten. Why not just call the "show()" function as we encounter the objects? Rather than add the objects to the object_array, and then at the very end going through the array and doing a 'show' on all, just do things more incrementally.

Now, there are possible downsides to this:
 - the "buffer using object_array" _can_ in theory result in at least 
   better I-cache usage (two tight loops rather than one more spread out 
   one). I don't think this is a real issue, but in theory..
 - this _does_ change the order of the objects printed. Instead of doing a 
   "process_tree(revs, commit->tree, &objects, NULL, "");" in the loop 
   over the commits (which puts all the root trees _first_ in the object 
   list, this patch just adds them to the list of pending objects, and 
   then we'll traverse them in that order (and thus show each root tree 
   object together with the objects we discover under it)
   I _think_ the new ordering actually makes more sense, but the object 
   ordering is actually a subtle thing when it comes to packing 
   efficiency, so any change in order is going to have implications for 
   packing. Good or bad, I dunno.
 - There may be some reason why we did it that odd way with the object 
   array, that I have simply forgotten.

Anyway, this includes the "free(name)" in builtin-pack-objects.c: show_object() logic, and now that we don't buffer up the objects before showing them that may actually result in lower memory usage during that whole traverse_commit_list() phase.

This is seriously not very deeply tested. It makes sense to me, it seems to pass all the tests, it looks ok, but...

Does anybody remember why we did that "object_array" thing? It used to be an "object_list" a long long time ago, but got changed into the array due to better memory usage patterns (those linked lists of obejcts are horrible from a memory allocation standpoint). But I wonder why we didn't do this back then. Maybe there's a reason for it.

Or maybe there _used_ to be a reason, and no longer is. 
			Linus
---
 builtin-pack-objects.c |   14 ++++++++++----
 builtin-rev-list.c     |   20 ++++++++++----------
 list-objects.c         |   35 ++++++++++++++++++-----------------
 list-objects.h         |    2 +-
 revision.c             |    2 +-
 revision.h             |    2 ++
 upload-pack.c          |   12 ++++++------
 7 files changed, 48 insertions(+), 39 deletions(-)
diff --git a/builtin-pack-objects.c b/builtin-pack-objects.c
index 9fc3b35..e028a02 100644
--- a/builtin-pack-objects.c
+++ b/builtin-pack-objects.c
@@ -1907,11 +1907,17 @@ static void show_commit(struct commit *commit)
 	commit->object.flags |= OBJECT_ADDED;
 }
 
-static void show_object(struct object_array_entry *p)
+static void show_object(struct object *obj, const char *name)
 {
-	add_preferred_base_object(p->name);
-	add_object_entry(p->item->sha1, p->item->type, p->name, 0);
-	p->item->flags |= OBJECT_ADDED;
+	add_preferred_base_object(name);
+	add_object_entry(obj->sha1, obj->type, name, 0);
+	obj->flags |= OBJECT_ADDED;
+
+	/*
+	 * We will have generated the hash from the name,
+	 * but not saved a pointer to it - we can free it
+	 */
+	free(name);
 }
 
 static void show_edge(struct commit *commit)
diff --git a/builtin-rev-list.c b/builtin-rev-list.c
index 40d5fcb..0815cf3 100644
--- a/builtin-rev-list.c
+++ b/builtin-rev-list.c
@@ -168,27 +168,27 @@ static void finish_commit(struct commit *commit)
 	commit->buffer = NULL;
 }
 
-static void finish_object(struct object_array_entry *p)
+static void finish_object(struct object *obj, const char *name)
 {
-	if (p->item->type == OBJ_BLOB && !has_sha1_file(p->item->sha1))
-		die("missing blob object '%s'", sha1_to_hex(p->item->sha1));
+	if (obj->type == OBJ_BLOB && !has_sha1_file(obj->sha1))
+		die("missing blob object '%s'", sha1_to_hex(obj->sha1));
 }
 
-static void show_object(struct object_array_entry *p)
+static void show_object(struct object *obj, const char *name)
 {
 	/* An object with name "foo\n0000000..." can be used to
 	 * confuse downstream "git pack-objects" very badly.
 	 */
-	const char *ep = strchr(p->name, '\n');
+	const char *ep = strchr(name, '\n');
 
-	finish_object(p);
+	finish_object(obj, name);
 	if (ep) {
-		printf("%s %.*s\n", sha1_to_hex(p->item->sha1),
-		       (int) (ep - p->name),
-		       p->name);
+		printf("%s %.*s\n", sha1_to_hex(obj->sha1),
+		       (int) (ep - name),
+		       name);
 	}
 	else
-		printf("%s %s\n", sha1_to_hex(p->item->sha1), p->name);
+		printf("%s %s\n", sha1_to_hex(obj->sha1), name);
 }
 
 static void show_edge(struct commit *commit)
diff --git a/list-objects.c b/list-objects.c
index dd243c7..5a4af62 100644
--- a/list-objects.c
+++ b/list-objects.c
@@ -10,7 +10,7 @@
 
 static void process_blob(struct rev_info *revs,
 			 struct blob *blob,
-			 struct object_array *p,
+			 show_object_fn show,
 			 struct name_path *path,
 			 const char *name)
 {
@@ -23,7 +23,7 @@ static void process_blob(struct rev_info *revs,
 	if (obj->flags & (UNINTERESTING | SEEN))
 		return;
 	obj->flags |= SEEN;
-	add_object(obj, p, path, name);
+	show(obj, path_name(path, name));
 }
 
 /*
@@ -50,7 +50,7 @@ static void process_blob(struct rev_info *revs,
  */
 static void process_gitlink(struct rev_info *revs,
 			    const unsigned char *sha1,
-			    struct object_array *p,
+			    show_object_fn show,
 			    struct name_path *path,
 			    const char *name)
 {
@@ -59,7 +59,7 @@ static void process_gitlink(struct rev_info *revs,
 
 static void process_tree(struct rev_info *revs,
 			 struct tree *tree,
-			 struct object_array *p,
+			 show_object_fn show,
 			 struct name_path *path,
 			 const char *name)
 {
@@ -77,7 +77,7 @@ static void process_tree(struct rev_info *revs,
 	if (parse_tree(tree) < 0)
 		die("bad tree object %s", sha1_to_hex(obj->sha1));
 	obj->flags |= SEEN;
-	add_object(obj, p, path, name);
+	show(obj, path_name(path, name));
 	me.up = path;
 	me.elem = name;
 	me.elem_len = strlen(name);
@@ -88,14 +88,14 @@ static void process_tree(struct rev_info *revs,
 		if (S_ISDIR(entry.mode))
 			process_tree(revs,
 				     lookup_tree(entry.sha1),
-				     p, &me, entry.path);
+				     show, &me, entry.path);
 		else if (S_ISGITLINK(entry.mode))
 			process_gitlink(revs, entry.sha1,
-					p, &me, entry.path);
+					show, &me, entry.path);
 		else
 			process_blob(revs,
 				     lookup_blob(entry.sha1),
-				     p, &me, entry.path);
+				     show, &me, entry.path);
 	}
 	free(tree->buffer);
 	tree->buffer = NULL;
@@ -134,16 +134,20 @@ void mark_edges_uninteresting(struct commit_list *list,
 	}
 }
 
+static void add_pending_tree(struct rev_info *revs, struct tree *tree)
+{
+	add_pending_object(revs, &tree->object, "");
+}
+
 void traverse_commit_list(struct rev_info *revs,
 			  void (*show_commit)(struct commit *),
-			  void (*show_object)(struct object_array_entry *))
+			  void (*show_object)(struct object *, const char *))
 {
 	int i;
 	struct commit *commit;
-	struct object_array objects = { 0, 0, NULL };
 
 	while ((commit = get_revision(revs)) != NULL) {
-		process_tree(revs, commit->tree, &objects, NULL, "");
+		add_pending_tree(revs, commit->tree);
 		show_commit(commit);
 	}
 	for (i = 0; i < revs->pending.nr; i++) {
@@ -154,25 +158,22 @@ void traverse_commit_list(struct rev_info *revs,
 			continue;
 		if (obj->type == OBJ_TAG) {
 			obj->flags |= SEEN;
-			add_object_array(obj, name, &objects);
+			show_object(obj, name);
 			continue;
 		}
 		if (obj->type == OBJ_TREE) {
-			process_tree(revs, (struct tree *)obj, &objects,
+			process_tree(revs, (struct tree *)obj, show_object,
 				     NULL, name);
 			continue;
 		}
 		if (obj->type == OBJ_BLOB) {
-			process_blob(revs, (struct blob *)obj, &objects,
+			process_blob(revs, (struct blob *)obj, show_object,
 				     NULL, name);
 			continue;
 		}
 		die("unknown pending object %s (%s)",
 		    sha1_to_hex(obj->sha1), name);
 	}
-	for (i = 0; i < objects.nr; i++)
-		show_object(&objects.objects[i]);
-	free(objects.objects);
 	if (revs->pending.nr) {
 		free(revs->pending.objects);
 		revs->pending.nr = 0;
diff --git a/list-objects.h b/list-objects.h
index 0f41391..13b0dd9 100644
--- a/list-objects.h
+++ b/list-objects.h
@@ -2,7 +2,7 @@
 #define LIST_OBJECTS_H
 
 typedef void (*show_commit_fn)(struct commit *);
-typedef void (*show_object_fn)(struct object_array_entry *);
+typedef void (*show_object_fn)(struct object *, const char *);
 typedef void (*show_edge_fn)(struct commit *);
 
 void traverse_commit_list(struct rev_info *revs, show_commit_fn, show_object_fn);
diff --git a/revision.c b/revision.c
index b6215cc..44a9ce2 100644
--- a/revision.c
+++ b/revision.c
@@ -15,7 +15,7 @@
 
 volatile show_early_output_fn_t show_early_output;
 
-static char *path_name(struct name_path *path, const char *name)
+char *path_name(struct name_path *path, const char *name)
 {
 	struct name_path *p;
 	char *n, *m;
diff --git a/revision.h b/revision.h
index 5adfc91..c89e8ff 100644
--- a/revision.h
+++ b/revision.h
@@ -146,6 +146,8 @@ struct name_path {
 	const char *elem;
 };
 
+char *path_name(struct name_path *path, const char *name);
+
 extern void add_object(struct object *obj,
 		       struct object_array *p,
 		       struct name_path *path,
diff --git a/upload-pack.c b/upload-pack.c
index a49d872..5524ac4 100644
--- a/upload-pack.c
+++ b/upload-pack.c
@@ -78,20 +78,20 @@ static void show_commit(struct commit *commit)
 	commit->buffer = NULL;
 }
 
-static void show_object(struct object_array_entry *p)
+static void show_object(struct object *obj, const char *name)
 {
 	/* An object with name "foo\n0000000..." can be used to
 	 * confuse downstream git-pack-objects very badly.
 	 */
-	const char *ep = strchr(p->name, '\n');
+	const char *ep = strchr(name, '\n');
 	if (ep) {
-		fprintf(pack_pipe, "%s %.*s\n", sha1_to_hex(p->item->sha1),
-		       (int) (ep - p->name),
-		       p->name);
+		fprintf(pack_pipe, "%s %.*s\n", sha1_to_hex(obj->sha1),
+		       (int) (ep - name),
+		       name);
 	}
 	else
 		fprintf(pack_pipe, "%s %s\n",
-				sha1_to_hex(p->item->sha1), p->name);
+				sha1_to_hex(obj->sha1), name);
 }
 
 static void show_edge(struct commit *commit)
Previous: Linus TorvaldsNext: Linus Torvalds
Message 57 of 97 in “Performance issue: initial git clone causes massive repack”
  1. Robin H. JohnsonApr 4, 2009
  2. Nicolas SebrechtApr 5, 2009
  3. Robin H. JohnsonApr 5, 2009
  4. Nicolas SebrechtApr 5, 2009
  5. Nicolas SebrechtApr 5, 2009
  6. Robin H. JohnsonApr 5, 2009
  7. Nicolas SebrechtApr 5, 2009
  8. Shawn O. PearceApr 5, 2009
  9. Robin H. JohnsonApr 5, 2009
  10. Robin H. JohnsonApr 5, 2009
  11. Shawn O. PearceApr 5, 2009
  12. david@lang.hmApr 5, 2009
  13. Sverre RabbelierApr 5, 2009
  14. Nicolas PitreApr 6, 2009
  15. Björn SteinbrinkApr 7, 2009
  16. Jakub NarebskiApr 7, 2009
  17. Nicolas PitreApr 7, 2009
  18. Jakub NarebskiApr 7, 2009
  19. Jon SmirlApr 7, 2009
  20. Nicolas PitreApr 7, 2009
  21. Björn SteinbrinkApr 7, 2009
  22. Nicolas PitreApr 7, 2009
  23. Björn SteinbrinkApr 7, 2009
  24. Nicolas PitreApr 7, 2009
  25. Björn SteinbrinkApr 7, 2009
  26. Nicolas PitreApr 8, 2009
  27. Robin H. JohnsonApr 10, 2009
  28. Nicolas PitreApr 11, 2009
  29. Mike HommeyApr 11, 2009
  30. Johannes SchindelinApr 14, 2009
  31. Nicolas PitreApr 14, 2009
  32. Robin H. JohnsonApr 14, 2009
  33. Nicolas PitreApr 14, 2009
  34. Nguyen Thai Ngoc DuyApr 15, 2009
  35. Robin H. JohnsonApr 15, 2009
  36. Junio C HamanoApr 15, 2009
  37. Nicolas PitreApr 15, 2009
  38. Sam VilainApr 22, 2009
  39. Mike RalphsonApr 22, 2009
  40. Pieter de BieApr 22, 2009
  41. Johannes SchindelinApr 22, 2009
  42. Shawn O. PearceApr 22, 2009
  43. Andreas EricssonApr 22, 2009
  44. Johannes SchindelinApr 22, 2009
  45. Christian CouderApr 23, 2009
  46. Nicolas PitreApr 22, 2009
  47. Sam VilainApr 22, 2009
  48. Björn SteinbrinkApr 22, 2009
  49. Nicolas PitreApr 22, 2009
  50. Johannes SchindelinApr 22, 2009
  51. Nicolas PitreApr 23, 2009
  52. Johannes SchindelinApr 14, 2009
  53. Jeff KingApr 7, 2009
  54. Björn SteinbrinkApr 7, 2009
  55. process_{tree,blob}: Remove useless xstrdup callsBjörn Steinbrink, Apr 8, 2009
  56. Linus TorvaldsApr 10, 2009
  57. Linus TorvaldsApr 11, 2009
  58. Linus TorvaldsApr 11, 2009
  59. Nicolas PitreApr 11, 2009
  60. Björn SteinbrinkApr 11, 2009
  61. Björn SteinbrinkApr 11, 2009
  62. Linus TorvaldsApr 11, 2009
  63. Linus TorvaldsApr 11, 2009
  64. Björn SteinbrinkApr 11, 2009
  65. Björn SteinbrinkApr 11, 2009
  66. Linus TorvaldsApr 11, 2009
  67. Björn SteinbrinkApr 11, 2009
  68. Linus TorvaldsApr 11, 2009
  69. Björn SteinbrinkApr 11, 2009
  70. Linus TorvaldsApr 11, 2009
  71. Nicolas SebrechtApr 5, 2009
  72. david@lang.hmApr 5, 2009
  73. Robin RosenbergApr 5, 2009
  74. Nicolas PitreApr 6, 2009
  75. Junio C HamanoApr 6, 2009
  76. Nicolas PitreApr 6, 2009
  77. Jon SmirlApr 6, 2009
  78. Nicolas PitreApr 6, 2009
  79. Jon SmirlApr 6, 2009
  80. Shawn O. PearceApr 6, 2009
  81. Nicolas PitreApr 6, 2009
  82. Jon SmirlApr 6, 2009
  83. Nicolas PitreApr 6, 2009
  84. Matthieu MoyApr 6, 2009
  85. Nicolas PitreApr 6, 2009
  86. Robin H. JohnsonApr 6, 2009
  87. Nicolas PitreApr 6, 2009
  88. Martin LanghoffApr 7, 2009
  89. Jeff KingApr 5, 2009
  90. Robin H. JohnsonApr 5, 2009
  91. Robin H. JohnsonApr 5, 2009
  92. Nguyen Thai Ngoc DuyApr 6, 2009
  93. Nicolas PitreApr 6, 2009
  94. Nicolas PitreApr 6, 2009
  95. Robin H. JohnsonApr 6, 2009
  96. Mark LevedahlApr 11, 2009
  97. Robin H. JohnsonApr 6, 2009

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