linux-kernel - Re: [PATCH 39/63] sched: numa: Use a system-wide search to find swap/migration candidates

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Date:	Mon, 07 Oct 2013 15:07:17 -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 39/63] sched: numa: Use a system-wide search to find swap/migration
 candidates

On 10/07/2013 06:29 AM, Mel Gorman wrote:
> This patch implements a system-wide search for swap/migration candidates
> based on total NUMA hinting faults. It has a balance limit, however it
> doesn't properly consider total node balance.
> 
> In the old scheme a task selected a preferred node based on the highest
> number of private faults recorded on the node. In this scheme, the preferred
> node is based on the total number of faults. If the preferred node for a
> task changes then task_numa_migrate will search the whole system looking
> for tasks to swap with that would improve both the overall compute
> balance and minimise the expected number of remote NUMA hinting faults.
> 
> Not there is no guarantee that the node the source task is placed
> on by task_numa_migrate() has any relationship to the newly selected
> task->numa_preferred_nid due to compute overloading.
> 
> [riel@...hat.com: Do not swap with tasks that cannot run on source cpu]
> 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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