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, 12 insertions, 1 deletions

diff --git a/tree.c b/tree.c
index 315b6a5d1..8b42a07b2 100644
--- a/tree.c
+++ b/tree.c
@@ -148,6 +148,7 @@ int parse_tree_buffer(struct tree *item, void *buffer, unsigned long size)
 {
 	void *bufptr = buffer;
 	struct tree_entry_list **list_p;
+	int n_refs = 0;
 
 	if (item->object.parsed)
 		return 0;
@@ -184,11 +185,21 @@ int parse_tree_buffer(struct tree *item, void *buffer, unsigned long size)
 			obj = &entry->item.blob->object;
 		}
 		if (obj)
-			add_ref(&item->object, obj);
+			n_refs++;
 		entry->parent = NULL; /* needs to be filled by the user */
 		*list_p = entry;
 		list_p = &entry->next;
 	}
+
+	if (track_object_refs) {
+		struct tree_entry_list *entry;
+		unsigned i = 0;
+		struct object_refs *refs = alloc_object_refs(n_refs);
+		for (entry = item->entries; entry; entry = entry->next)
+			refs->ref[i++] = entry->item.any;
+		set_object_refs(&item->object, refs);
+	}
+
 	return 0;
 }