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Subject[ 07/40] mm/vmstat.c: cache align vm_stat
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From: Greg KH <gregkh@linuxfoundation.org>

3.0-stable review patch. If anyone has any objections, please let me know.

------------------

From: Dimitri Sivanich <sivanich@sgi.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.

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@sgi.com>
Acked-by: Christoph Lameter <cl@gentwo.org>
Acked-by: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Mel Gorman <mgorman@suse.de>

---
mm/vmstat.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- 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



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