linux-kernel - Re: [patch v3] mm, thp: only collapse hugepages to nodes with affinity for zone_reclaim

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Message-ID: <53D60CDD.4080801@suse.cz>
Date:	Mon, 28 Jul 2014 10:42:05 +0200
From:	Vlastimil Babka <vbabka@...e.cz>
To:	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>
CC:	Andrea Arcangeli <aarcange@...hat.com>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Bob Liu <bob.liu@...cle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch v3] mm, thp: only collapse hugepages to nodes with affinity
 for zone_reclaim_mode

On 07/17/2014 02:59 AM, David Rientjes wrote:
> Commit 9f1b868a13ac ("mm: thp: khugepaged: add policy for finding target
> node") improved the previous khugepaged logic which allocated a
> transparent hugepages from the node of the first page being collapsed.
>
> However, it is still possible to collapse pages to remote memory which may
> suffer from additional access latency.  With the current policy, it is
> possible that 255 pages (with PAGE_SHIFT == 12) will be collapsed remotely
> if the majority are allocated from that node.
>
> When zone_reclaim_mode is enabled, it means the VM should make every attempt
> to allocate locally to prevent NUMA performance degradation.  In this case,
> we do not want to collapse hugepages to remote nodes that would suffer from
> increased access latency.  Thus, when zone_reclaim_mode is enabled, only
> allow collapsing to nodes with RECLAIM_DISTANCE or less.
>
> There is no functional change for systems that disable zone_reclaim_mode.
>
> Signed-off-by: David Rientjes <rientjes@...gle.com>

Acked-by: Vlastimil Babka <vbabka@...e.cz>

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