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

[Johannes Weiner]

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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