mm: remove alignment padding from anon_vma on (some) 64 bit builds

Reorder structure anon_vma to remove alignment padding on 64 builds when
(CONFIG_KSM || CONFIG_MIGRATION).
This will shrink the size of the anon_vma structure from 40 to 32 bytes
& allow more objects per slab in its kmem_cache.

Under slub the objects in the anon_vma kmem_cache will then be 40 bytes
with 102 objects per slab.  (On v2.6.36 without this patch,the size is 48
bytes and 85 objects/slab.)

Signed-off-by: Richard Kennedy <richard@rsk.demon.co.uk>
Reviewed-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 31b2fd7..5c98df6 100644 (file)
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -25,8 +25,8 @@
  * pointing to this anon_vma once its vma list is empty.
  */
 struct anon_vma {
-       spinlock_t lock;        /* Serialize access to vma list */
        struct anon_vma *root;  /* Root of this anon_vma tree */
+       spinlock_t lock;        /* Serialize access to vma list */
 #if defined(CONFIG_KSM) || defined(CONFIG_MIGRATION)
 
        /*