Re: [PATCH] Reduce vm_stat cacheline contention in__vm_enough_memory

[Christoph Lameter]

On Thu, 13 Oct 2011, Dimitri Sivanich wrote:

> > increase the allowed delta per zone if frequent updates occur via the
> > overflow checks in vmstat.c. See calculate_*_threshold there.
>
> I tried changing the threshold in both directions, with slower throughput in
> both cases.

If that is the case check for the vm_stat cacheline being shared with
another hot kernel variable variable. Maybe that causes cacheline
eviction.

If there are no updates occurring for a while (due to increased deltas
and/or vmstat updates) then the vm_stat cacheline should be able to stay
in shared mode in multiple processors and the performance should increase.


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