linux-kernel - Re: [PATCH 0/2] Disable zone_reclaim

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Date:	Tue, 8 Apr 2014 09:17:04 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Vlastimil Babka <vbabka@...e.cz>
cc:	Mel Gorman <mgorman@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Robert Haas <robertmhaas@...il.com>,
	Josh Berkus <josh@...iodbs.com>,
	Andres Freund <andres@...quadrant.com>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>, sivanich@....com
Subject: Re: [PATCH 0/2] Disable zone_reclaim_mode by default

On Tue, 8 Apr 2014, Vlastimil Babka wrote:

> On 04/08/2014 12:34 AM, Mel Gorman wrote:
> > When it was introduced, zone_reclaim_mode made sense as NUMA distances
> > punished and workloads were generally partitioned to fit into a NUMA
> > node. NUMA machines are now common but few of the workloads are NUMA-aware
> > and it's routine to see major performance due to zone_reclaim_mode being
> > disabled but relatively few can identify the problem.
>     ^ I think you meant "enabled" here?
>
> Just in case the cover letter goes to the changelog...

Correct.

Another solution here would be to increase the threshhold so that
4 socket machines do not enable zone reclaim by default. The larger the
NUMA system is the more memory is off node from the perspective of a
processor and the larger the hit from remote memory.

On the other hand: The more expensive we make reclaim the less it
makes sense to allow zone reclaim to occur.

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