linux-kernel - Re: [PATCH 13/63] sched: numa: Mitigate chance that same task always updates PTEs

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Message-ID: <5252EE4A.1060904@redhat.com>
Date:	Mon, 07 Oct 2013 13:24:26 -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 13/63] sched: numa: Mitigate chance that same task always
 updates PTEs

On 10/07/2013 06:28 AM, Mel Gorman wrote:
> From: Peter Zijlstra <peterz@...radead.org>
> 
> With a trace_printk("working\n"); right after the cmpxchg in
> task_numa_work() we can see that of a 4 thread process, its always the
> same task winning the race and doing the protection change.
> 
> This is a problem since the task doing the protection change has a
> penalty for taking faults -- it is busy when marking the PTEs. If its
> always the same task the ->numa_faults[] get severely skewed.
> 
> Avoid this by delaying the task doing the protection change such that
> it is unlikely to win the privilege again.

> Signed-off-by: Peter Zijlstra <peterz@...radead.org>
> Signed-off-by: Mel Gorman <mgorman@...e.de>

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

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