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[PATCH v3 18/21] packed_ref_store: get rid of the `ref_cache` entirely

From
Michael Haggerty <mhagger@alum.mit.edu>
Date
Sep 25, 2017, 08:00 UTC
Message-ID
<cfa2e29c34bb712b17b8067515710a606a4fedab.1506325610.git.mhagger@alum.mit.edu>
In-Reply-To
<cover.1506325610.git.mhagger@alum.mit.edu>

Now that everything has been changed to read what it needs directly out of the `packed-refs` file, `packed_ref_store` doesn't need to maintain a `ref_cache` at all. So get rid of it.

First of all, this will save a lot of memory and lots of little allocations. Instead of needing to store complicated parsed data structures in memory, we just mmap the file (potentially sharing memory with other processes) and parse only what we need.

Moreover, since the mmapped access to the file reads only the parts of the file that it needs, this might save reading all of the data from disk at all (at least if the file starts out sorted).

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
---
 refs/packed-backend.c | 29 ++---------------------------
 1 file changed, 2 insertions(+), 27 deletions(-)
diff --git a/refs/packed-backend.c b/refs/packed-backend.c
index dbbba45502..3829e9c294 100644
--- a/refs/packed-backend.c
+++ b/refs/packed-backend.c
@@ -45,8 +45,6 @@ struct packed_ref_cache {
 	 */
 	struct packed_ref_store *refs;
 
-	struct ref_cache *cache;
-
 	/* Is the `packed-refs` file currently mmapped? */
 	int mmapped;
 
@@ -148,7 +146,6 @@ static void release_packed_ref_buffer(struct packed_ref_cache *packed_refs)
 static int release_packed_ref_cache(struct packed_ref_cache *packed_refs)
 {
 	if (!--packed_refs->referrers) {
-		free_ref_cache(packed_refs->cache);
 		stat_validity_clear(&packed_refs->validity);
 		release_packed_ref_buffer(packed_refs);
 		free(packed_refs);
@@ -719,15 +716,10 @@ static const char *find_reference_location(struct packed_ref_cache *cache,
 static struct packed_ref_cache *read_packed_refs(struct packed_ref_store *refs)
 {
 	struct packed_ref_cache *packed_refs = xcalloc(1, sizeof(*packed_refs));
-	struct ref_dir *dir;
-	struct ref_iterator *iter;
 	int sorted = 0;
-	int ok;
 
 	packed_refs->refs = refs;
 	acquire_packed_ref_cache(packed_refs);
-	packed_refs->cache = create_ref_cache(NULL, NULL);
-	packed_refs->cache->root->flag &= ~REF_INCOMPLETE;
 	packed_refs->peeled = PEELED_NONE;
 
 	if (!load_contents(packed_refs))
@@ -800,23 +792,6 @@ static struct packed_ref_cache *read_packed_refs(struct packed_ref_store *refs)
 		packed_refs->eof = buf_copy + size;
 	}
 
-	dir = get_ref_dir(packed_refs->cache->root);
-	iter = mmapped_ref_iterator_begin(
-			packed_refs,
-			packed_refs->buf + packed_refs->header_len,
-			packed_refs->eof);
-	while ((ok = ref_iterator_advance(iter)) == ITER_OK) {
-		struct ref_entry *entry =
-			create_ref_entry(iter->refname, iter->oid, iter->flags);
-
-		if ((iter->flags & REF_KNOWS_PEELED))
-			ref_iterator_peel(iter, &entry->u.value.peeled);
-		add_ref_entry(dir, entry);
-	}
-
-	if (ok != ITER_DONE)
-		die("error reading packed-refs file %s", refs->path);
-
 	return packed_refs;
 }
 
@@ -975,8 +950,8 @@ static struct ref_iterator *packed_ref_iterator_begin(
 	else
 		start = packed_refs->buf + packed_refs->header_len;
 
-	iter->iter0 = mmapped_ref_iterator_begin(
-			packed_refs, start, packed_refs->eof);
+	iter->iter0 = mmapped_ref_iterator_begin(packed_refs,
+						 start, packed_refs->eof);
 
 	iter->flags = flags;
 

-- 
2.14.1
Previous: Michael HaggertyNext: Michael Haggerty
Message 19 of 24 in “Read `packed-refs` using mmap()”
  1. 00/21 Read `packed-refs` using mmap()Michael Haggerty, Sep 25, 2017
  2. 01/21 ref_iterator: keep track of whether the iterator output is orderedMichael Haggerty, Sep 25, 2017
  3. 02/21 prefix_ref_iterator: break when we leave the prefixMichael Haggerty, Sep 25, 2017
  4. 03/21 packed_ref_cache: add a backlink to the associated `packed_ref_store`Michael Haggerty, Sep 25, 2017
  5. 04/21 die_unterminated_line(), die_invalid_line(): new functionsMichael Haggerty, Sep 25, 2017
  6. 05/21 read_packed_refs(): use mmap to read the `packed-refs` fileMichael Haggerty, Sep 25, 2017
  7. 06/21 read_packed_refs(): only check for a header at the top of the fileMichael Haggerty, Sep 25, 2017
  8. 07/21 read_packed_refs(): make parsing of the header line more robustMichael Haggerty, Sep 25, 2017
  9. 09/21 packed_ref_cache: remember the file-wide peeling stateMichael Haggerty, Sep 25, 2017
  10. 08/21 read_packed_refs(): read references with minimal copyingMichael Haggerty, Sep 25, 2017
  11. 10/21 mmapped_ref_iterator: add iterator over a packed-refs fileMichael Haggerty, Sep 25, 2017
  12. 12/21 packed-backend.c: reorder some definitionsMichael Haggerty, Sep 25, 2017
  13. 13/21 packed_ref_cache: keep the `packed-refs` file mmapped if possibleMichael Haggerty, Sep 25, 2017
  14. 14/21 read_packed_refs(): ensure that references are ordered when readMichael Haggerty, Sep 25, 2017
  15. 11/21 mmapped_ref_iterator_advance(): no peeled value for broken refsMichael Haggerty, Sep 25, 2017
  16. 15/21 packed_ref_iterator_begin(): iterate using `mmapped_ref_iterator`Michael Haggerty, Sep 25, 2017
  17. 16/21 packed_read_raw_ref(): read the reference from the mmapped bufferMichael Haggerty, Sep 25, 2017
  18. 17/21 ref_store: implement `refs_peel_ref()` genericallyMichael Haggerty, Sep 25, 2017
  19. 18/21 packed_ref_store: get rid of the `ref_cache` entirelyMichael Haggerty, Sep 25, 2017
  20. 20/21 mmapped_ref_iterator: inline into `packed_ref_iterator`Michael Haggerty, Sep 25, 2017
  21. 19/21 ref_cache: remove support for storing peeled valuesMichael Haggerty, Sep 25, 2017
  22. 21/21 packed-backend.c: rename a bunch of things and update commentsMichael Haggerty, Sep 25, 2017
  23. Jeff KingSep 25, 2017
  24. Junio C HamanoSep 29, 2017

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