linux-kernel - [PATCH] mm: remove alignment padding from anon

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Date:	Sat, 28 Aug 2010 15:09:46 +0100
From:	Richard Kennedy <richard@....demon.co.uk>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-mm <linux-mm@...ck.org>, lkml <linux-kernel@...r.kernel.org>,
	Rik van Riel <riel@...hat.com>
Subject: [PATCH] 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.)
    
compiled & tested on x86_64 using SLUB
    
Signed-off-by: Richard Kennedy <richard@....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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