linux-kernel - Re: [PATCH] Reduce vm_stat cacheline contention in __vm_enough

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Message-ID: <alpine.DEB.2.00.1110131052300.18473@router.home>
Date:	Thu, 13 Oct 2011 10:54:30 -0500 (CDT)
From:	Christoph Lameter <cl@...two.org>
To:	Dimitri Sivanich <sivanich@....com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Mel Gorman <mel@....ul.ie>
Subject: Re: [PATCH] Reduce vm_stat cacheline contention in
 __vm_enough_memory

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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