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SubjectRe: [PATCH] Reduce vm_stat cacheline contention in __vm_enough_memory
On Thu, 13 Oct 2011 10:54:30 -0500 (CDT)
Christoph Lameter <cl@gentwo.org> wrote:

> 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.

yup. `nm -n vmlinux'.

> 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.
>

We could cacheline align vm_stat[]. But the thing is pretty small - we
couild put each entry in its own cacheline.




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