ocfs2: allocation hints

Record the most recently used allocation group on the allocation context, so
that subsequent allocations can attempt to optimize for contiguousness.
Local alloc especially should benefit from this as the current chain search
tends to let it spew across the disk.

Signed-off-by: Mark Fasheh <mark.fasheh@oracle.com>

fs/ocfs2/suballoc.h

@@ -49,6 +49,8 @@ struct ocfs2_alloc_context {
 	u16    ac_chain;
 	int    ac_allow_chain_relink;
 	group_search_t *ac_group_search;
+
+	u64    ac_last_group;
 };
 
 void ocfs2_free_alloc_context(struct ocfs2_alloc_context *ac);