Rework object refs tracking to reduce memory usage

Store pointers to referenced objects in a variable sized array instead
of linked list.  This cuts down memory usage of utilities which use
object references; e.g., git-fsck-objects --full on the git.git
repository consumes about 2 MB of memory tracked by Massif instead of
7 MB before the change.  Object refs are still the biggest consumer of
memory (57%), but the malloc overhead for a single block instead of a
linked list is substantially smaller.

Signed-off-by: Sergey Vlasov <vsu@altlinux.ru>
Signed-off-by: Junio C Hamano <junkio@cox.net>

1 files changed, 5 insertions, 2 deletions

diff --git a/tag.c b/tag.c
index e574c4b..61ac434 100644
--- a/tag.c
+++ b/tag.c
@@ -75,8 +75,11 @@ int parse_tag_buffer(struct tag *item, void *data, unsigned long size)
 	item->tag[taglen] = '\0';
 
 	item->tagged = lookup_object_type(object, type);
-	if (item->tagged)
-		add_ref(&item->object, item->tagged);
+	if (item->tagged && track_object_refs) {
+		struct object_refs *refs = alloc_object_refs(1);
+		refs->ref[0] = item->tagged;
+		set_object_refs(&item->object, refs);
+	}
 
 	return 0;
 }