linux-kernel - [PATCH] cache align vm

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Date:	Mon, 24 Oct 2011 11:10:35 -0500
From:	Dimitri Sivanich <sivanich@....com>
To:	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <cl@...two.org>,
	David Rientjes <rientjes@...gle.com>,
	Andi Kleen <andi@...stfloor.org>, Mel Gorman <mel@....ul.ie>
Subject: [PATCH] cache align vm_stat

Avoid false sharing of the vm_stat array.

This was found to adversely affect tmpfs I/O performance.

Signed-off-by: Dimitri Sivanich <sivanich@....com>
---
 mm/vmstat.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux/mm/vmstat.c
===================================================================
--- linux.orig/mm/vmstat.c
+++ linux/mm/vmstat.c
@@ -78,7 +78,7 @@ void vm_events_fold_cpu(int cpu)
  *
  * vm_stat contains the global counters
  */
-atomic_long_t vm_stat[NR_VM_ZONE_STAT_ITEMS];
+atomic_long_t vm_stat[NR_VM_ZONE_STAT_ITEMS] __cacheline_aligned_in_smp;
 EXPORT_SYMBOL(vm_stat);
 
 #ifdef CONFIG_SMP
--
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