linux-kernel - Re: [PATCH 5/9] numa,sched,mm: use active_nodes nodemask to limit numa migrations

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Date:	Tue, 28 Jan 2014 09:58:28 +0000
From:	Mel Gorman <mgorman@...e.de>
To:	riel@...hat.com
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	peterz@...radead.org, mingo@...hat.com, chegu_vinod@...com
Subject: Re: [PATCH 5/9] numa,sched,mm: use active_nodes nodemask to limit
 numa migrations

On Mon, Jan 27, 2014 at 05:03:44PM -0500, riel@...hat.com wrote:
> From: Rik van Riel <riel@...hat.com>
> 
> Use the active_nodes nodemask to make smarter decisions on NUMA migrations.
> 
> In order to maximize performance of workloads that do not fit in one NUMA
> node, we want to satisfy the following criteria:
> 1) keep private memory local to each thread
> 2) avoid excessive NUMA migration of pages
> 3) distribute shared memory across the active nodes, to
>    maximize memory bandwidth available to the workload
> 
> This patch accomplishes that by implementing the following policy for
> NUMA migrations:
> 1) always migrate on a private fault
> 2) never migrate to a node that is not in the set of active nodes
>    for the numa_group
> 3) always migrate from a node outside of the set of active nodes,
>    to a node that is in that set
> 4) within the set of active nodes in the numa_group, only migrate
>    from a node with more NUMA page faults, to a node with fewer
>    NUMA page faults, with a 25% margin to avoid ping-ponging
> 
> This results in most pages of a workload ending up on the actively
> used nodes, with reduced ping-ponging of pages between those nodes.
> 
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Mel Gorman <mgorman@...e.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Chegu Vinod <chegu_vinod@...com>
> Signed-off-by: Rik van Riel <riel@...hat.com>

Acked-by: Mel Gorman <mgorman@...e.de>

-- 
Mel Gorman
SUSE Labs
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