Optimize sha1_object_info for loose objects, not concurrent repacks

When dealing with a repository with lots of loose objects, sha1_object_info
would rescan the packs directory every time an unpacked object was referenced
before finally giving up and looking for the loose object. This caused a lot
of extra unnecessary system calls during git pack-objects; the code was
rereading the entire pack directory once for each loose object file.

This patch looks for a loose object before falling back to rescanning the
pack directory, rather than the other way around.

Signed-off-by: Steven Grimm <koreth@midwinter.com>
Acked-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

sha1_file.c

@@ -1929,11 +1929,18 @@ static int sha1_loose_object_info(const unsigned char *sha1, unsigned long *size
 int sha1_object_info(const unsigned char *sha1, unsigned long *sizep)
 {
 	struct pack_entry e;
+	int status;
 
 	if (!find_pack_entry(sha1, &e, NULL)) {
+		/* Most likely it's a loose object. */
+		status = sha1_loose_object_info(sha1, sizep);
+		if (status >= 0)
+			return status;
+
+		/* Not a loose object; someone else may have just packed it. */
 		reprepare_packed_git();
 		if (!find_pack_entry(sha1, &e, NULL))
-			return sha1_loose_object_info(sha1, sizep);
+			return status;
 	}
 	return packed_object_info(e.p, e.offset, sizep);
 }