linux-kernel - Re: [PATCH 1/2] mm: Disable zone_reclaim

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Date:	Tue, 8 Apr 2014 15:47:35 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Christoph Lameter <cl@...ux.com>
Cc:	sivanich@....com, 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>
Subject: Re: [PATCH 1/2] mm: Disable zone_reclaim_mode by default

On Tue, Apr 08, 2014 at 09:14:05AM -0500, Christoph Lameter wrote:
> On Mon, 7 Apr 2014, Mel Gorman wrote:
> 
> > zone_reclaim_mode causes processes to prefer reclaiming memory from local
> > node instead of spilling over to other nodes. This made sense initially when
> > NUMA machines were almost exclusively HPC and the workload was partitioned
> > into nodes. The NUMA penalties were sufficiently high to justify reclaiming
> > the memory. On current machines and workloads it is often the case that
> > zone_reclaim_mode destroys performance but not all users know how to detect
> > this. Favour the common case and disable it by default. Users that are
> > sophisticated enough to know they need zone_reclaim_mode will detect it.
> 
> Ok that is going to require SGI machines to deal with zone_reclaim
> configurations on bootup. Dimitri? Any comments?
> 

The SGI machines are also likely to be managed by system administrators
who are both aware of zone_reclaim_mode and know how to evaluate if it
should be enabled or not. The pair of patches is really aimmed at the
common case of 2-8 socket machines running workloads that are not NUMA
aware.

-- 
Mel Gorman
SUSE Labs
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