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

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

[Richard Kennedy]

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.)
    
compiled & tested on x86_64 using SLUB
    
Signed-off-by: Richard Kennedy <richard@rsk.demon.co.uk>
---
patch against v2.6.36-rc2
compiled & tested on x86_64 AMD X2  

regards
Richard


diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 31b2fd7..5c98df6 100644
--- 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)
 
 	/*


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Re: [PATCH] mm: remove alignment padding from anon_vma on (some) 64 bit builds

[Rik van Riel]

On 08/28/2010 10:09 AM, Richard Kennedy wrote:
> 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.)
>
> compiled&  tested on x86_64 using SLUB
>
> Signed-off-by: Richard Kennedy<richard@rsk.demon.co.uk>

Reviewed-by: Rik van Riel <riel@redhat.com>

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