Remove "refs" field from "struct object"

This shrinks "struct object" to the absolutely minimal size possible.
It now contains /only/ the object flags and the SHA1 hash name of the
object.

The "refs" field, which is really needed only for fsck, is maintained in
a separate hashed lookup-table, allowing all normal users to totally
ignore it.

This helps memory usage, although not as much as I hoped: it looks like
the allocation overhead of malloc (and the alignment constraints in
particular) means that while the structure size shrinks, the actual
allocation overhead mostly does not.

[ That said: memory usage is actually down, but not as much as it should
  be: I suspect just one of the object types actually ended up shrinking
  its effective allocation size.

  To get to the next level, we probably need specialized allocators that
  don't pad the allocation more than necessary. ]

The separation makes for some code cleanup, though, and makes the ref
tracking that fsck wants a clearly separate thing.

Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

1 files changed, 3 insertions, 1 deletions

diff --git a/object.h b/object.h
index f4ee2e5..c537b4b 100644
--- a/object.h
+++ b/object.h
@@ -9,6 +9,7 @@ struct object_list {
 
 struct object_refs {
 	unsigned count;
+	struct object *base;
 	struct object *ref[FLEX_ARRAY]; /* more */
 };
 
@@ -28,7 +29,6 @@ struct object {
 	unsigned type : TYPE_BITS;
 	unsigned flags : FLAG_BITS;
 	unsigned char sha1[20];
-	struct object_refs *refs;
 };
 
 extern int track_object_refs;
@@ -41,6 +41,8 @@ static inline const char *typename(unsigned int type)
 	return type_names[type > TYPE_TAG ? TYPE_BAD : type];
 }
 
+extern struct object_refs *lookup_object_refs(struct object *);
+
 /** Internal only **/
 struct object *lookup_object(const unsigned char *sha1);