linux-kernel - [PATCH 01/34] mm: vmstat: cache align vm

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Date:	Mon, 23 Jul 2012 14:38:14 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Stable <stable@...r.kernel.org>
Cc:	Linux-MM <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>,
	Mel Gorman <mgorman@...e.de>
Subject: [PATCH 01/34] mm: vmstat: cache align vm_stat

From: Dimitri Sivanich <sivanich@....com>

commit a1cb2c60ddc98ff4e5246f410558805401ceee67 upstream.

Stable note: Not tracked on Bugzilla. This patch is known to make a big
	difference to tmpfs performance on larger machines.

Avoid false sharing of the vm_stat array. This was found to adversely
affect tmpfs I/O performance.

Tests run on a 640 cpu UV system.

With 120 threads doing parallel writes, each to different tmpfs mounts:
No patch:		~300 MB/sec
With vm_stat alignment:	~430 MB/sec

Signed-off-by: Dimitri Sivanich <sivanich@....com>
Acked-by: Christoph Lameter <cl@...two.org>
Acked-by: Mel Gorman <mel@....ul.ie>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Mel Gorman <mgorman@...e.de>
---
 mm/vmstat.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/vmstat.c b/mm/vmstat.c
index 20c18b7..6559013 100644
--- a/mm/vmstat.c
+++ b/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
-- 
1.7.9.2

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