[PATCH] page_uptodate locking scalability

Use a bit spin lock in the first buffer of the page to synchronise asynch
IO buffer completions, instead of the global page_uptodate_lock, which is
showing some scalabilty problems.

Signed-off-by: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
index 802c91e9b3da..90828493791f 100644
--- a/include/linux/buffer_head.h
+++ b/include/linux/buffer_head.h
@@ -19,6 +19,9 @@ enum bh_state_bits {
         BH_Dirty,       /* Is dirty */
         BH_Lock,        /* Is locked */
         BH_Req,         /* Has been submitted for I/O */
+        BH_Uptodate_Lock,/* Used by the first bh in a page, to serialise
+                          * IO completion of other buffers in the page
+                          */
 
         BH_Mapped,      /* Has a disk mapping */
         BH_New,         /* Disk mapping was newly created by get_block */