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

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Message-ID: <alpine.DEB.2.00.1110140932530.6411@router.home>
Date:	Fri, 14 Oct 2011 09:34:17 -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 Fri, 14 Oct 2011, Dimitri Sivanich wrote:

> Increasing the ZVC deltas (threshold value in calculate*threshold == 125)
> does -seem- to give a small speedup in this case (maybe as much as 50 MB/sec?).

Hmm... The question is how much do the VM paths used for the critical path
increment the vmstat counters on average per second? If we end up with
hundred of updates per second from each thread then we still have a
problem that can only be addressed by increasing the deltas beyond 125
meaning the fieldwidth must be increased to support 16 bit counters.

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