linux-kernel - Re: [PATCH] mm, numa: Really disable NUMA balancing by default on single node machines

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Date:	Wed, 13 May 2015 09:07:46 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Mel Gorman <mgorman@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>
CC:	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm, numa: Really disable NUMA balancing by default on
 single node machines

On 05/13/2015 04:10 AM, Mel Gorman wrote:
> NUMA balancing is meant to be disabled by default on UMA machines but
> the check is using nr_node_ids (highest node) instead of num_online_nodes
> (online nodes). The consequences are that a UMA machine with a node ID of 1
> or higher will enable NUMA balancing. This will incur useless overhead due
> to minor faults with the impact depending on the workload. These are the
> impact on the stats when running a kernel build on a single node machine
> whose node ID happened to be 1;
> 
> 			       vanilla     patched
> NUMA base PTE updates          5113158           0
> NUMA huge PMD updates              643           0
> NUMA page range updates        5442374           0
> NUMA hint faults               2109622           0
> NUMA hint local faults         2109622           0
> NUMA hint local percent            100         100
> NUMA pages migrated                  0           0
> 
> Signed-off-by: Mel Gorman <mgorman@...e.de>
> Cc: <stable@...r.kernel.org> #v3.8+

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

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