Re: [PATCH 3/6] mm: Move zone->pages_scanned into a vmstat counter

From: Johannes Weiner
Date: Thu Jul 10 2014 - 08:09:07 EST

On Wed, Jul 09, 2014 at 09:13:05AM +0100, Mel Gorman wrote:
> zone->pages_scanned is a write-intensive cache line during page reclaim
> and it's also updated during page free. Move the counter into vmstat to
> take advantage of the per-cpu updates and do not update it in the free
> paths unless necessary.
> On a small UMA machine running tiobench the difference is marginal. On a
> 4-node machine the overhead is more noticable. Note that automatic NUMA
> balancing was disabled for this test as otherwise the system CPU overhead
> is unpredictable.
> 3.16.0-rc3 3.16.0-rc3 3.16.0-rc3
> vanillarearrange-v5 vmstat-v5
> User 746.94 759.78 774.56
> System 65336.22 58350.98 32847.27
> Elapsed 27553.52 27282.02 27415.04
> Note that the overhead reduction will vary depending on where exactly
> pages are allocated and freed.
> Signed-off-by: Mel Gorman <mgorman@xxxxxxx>

Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
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