linux-kernel - Re: [PATCH] mm: numa: Return the number of base pages altered by protection changes

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Date:	Sun, 10 Nov 2013 19:22:57 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Mel Gorman <mgorman@...e.de>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Alex Thorlton <athorlton@....com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] mm: numa: Return the number of base pages altered by
 protection changes

On 11/09/2013 09:37 AM, Mel Gorman wrote:
> Commit 0255d491 (mm: Account for a THP NUMA hinting update as one PTE
> update) was added to account for the number of PTE updates when marking
> pages prot_numa. task_numa_work was using the old return value to track
> how much address space had been updated. Altering the return value causes
> the scanner to do more work than it is configured or documented to in a
> single unit of work.
> 
> This patch reverts 0255d491 and accounts for the number of THP updates
> separately in vmstat. It is up to the administrator to interpret the pair
> of values correctly. This is a straight-forward operation and likely to
> only be of interest when actively debugging NUMA balancing problems.
> 
> The impact of this patch is that the NUMA PTE scanner will scan slower when
> THP is enabled and workloads may converge slower as a result. On the flip
> size system CPU usage should be lower than recent tests reported. This is
> an illustrative example of a short single JVM specjbb test

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


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