linux-kernel - Re: [PATCH 21/63] sched: Update NUMA hinting faults once per scan

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Date:	Mon, 07 Oct 2013 14:39:20 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Mel Gorman <mgorman@...e.de>
CC:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...nel.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 21/63] sched: Update NUMA hinting faults once per scan

On 10/07/2013 06:28 AM, Mel Gorman wrote:
> NUMA hinting fault counts and placement decisions are both recorded in the
> same array which distorts the samples in an unpredictable fashion. The values
> linearly accumulate during the scan and then decay creating a sawtooth-like
> pattern in the per-node counts. It also means that placement decisions are
> time sensitive. At best it means that it is very difficult to state that
> the buffer holds a decaying average of past faulting behaviour. At worst,
> it can confuse the load balancer if it sees one node with an artifically high
> count due to very recent faulting activity and may create a bouncing effect.
> 
> This patch adds a second array. numa_faults stores the historical data
> which is used for placement decisions. numa_faults_buffer holds the
> fault activity during the current scan window. When the scan completes,
> numa_faults decays and the values from numa_faults_buffer are copied
> across.
> 
> Signed-off-by: Mel Gorman <mgorman@...e.de>

Reviewed-by: Rik van Riel <riel@...hat.com>


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