packed_ref_store: get rid of the ref_cache entirely

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 <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: mhagger

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;