[PATCH] don't load and decompress objects twice with parse_object()

It turns out that parse_object() is loading and decompressing given
object to free it just before calling the specific object parsing
function which does mmap and decompress the same object again. This
patch introduces the ability to parse specific objects directly from a
memory buffer.

Without this patch, running git-fsck-cache on the kernel repositorytake:

	real    0m13.006s
	user    0m11.421s
	sys     0m1.218s

With this patch applied:

	real    0m8.060s
	user    0m7.071s
	sys     0m0.710s

The performance increase is significant, and this is kind of a
prerequisite for sane delta object support with fsck.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 16 insertions, 14 deletions

diff --git a/object.c b/object.c
index c1f22910a2..b5a62e7f87 100644
--- a/object.c
+++ b/object.c
@@ -104,6 +104,7 @@ struct object *parse_object(unsigned char *sha1)
 	unsigned long mapsize;
 	void *map = map_sha1_file(sha1, &mapsize);
 	if (map) {
+		struct object *obj;
 		char type[100];
 		unsigned long size;
 		void *buffer = unpack_sha1_file(map, mapsize, type, &size);
@@ -112,26 +113,27 @@ struct object *parse_object(unsigned char *sha1)
 			return NULL;
 		if (check_sha1_signature(sha1, buffer, size, type) < 0)
 			printf("sha1 mismatch %s\n", sha1_to_hex(sha1));
-		free(buffer);
 		if (!strcmp(type, "blob")) {
-			struct blob *ret = lookup_blob(sha1);
-			parse_blob(ret);
-			return &ret->object;
+			struct blob *blob = lookup_blob(sha1);
+			parse_blob_buffer(blob, buffer, size);
+			obj = &blob->object;
 		} else if (!strcmp(type, "tree")) {
-			struct tree *ret = lookup_tree(sha1);
-			parse_tree(ret);
-			return &ret->object;
+			struct tree *tree = lookup_tree(sha1);
+			parse_tree_buffer(tree, buffer, size);
+			obj = &tree->object;
 		} else if (!strcmp(type, "commit")) {
-			struct commit *ret = lookup_commit(sha1);
-			parse_commit(ret);
-			return &ret->object;
+			struct commit *commit = lookup_commit(sha1);
+			parse_commit_buffer(commit, buffer, size);
+			obj = &commit->object;
 		} else if (!strcmp(type, "tag")) {
-			struct tag *ret = lookup_tag(sha1);
-			parse_tag(ret);
-			return &ret->object;
+			struct tag *tag = lookup_tag(sha1);
+			parse_tag_buffer(tag, buffer, size);
+			obj = &tag->object;
 		} else {
-			return NULL;
+			obj = NULL;
 		}
+		free(buffer);
+		return obj;
 	}
 	return NULL;
 }