From: Dimitri Sivanich <redacted>

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 <redacted>
Acked-by: Christoph Lameter <cl@gentwo.org>
Acked-by: Mel Gorman <redacted>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Mel Gorman <mgorman@suse.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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