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

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Message-ID: <20140408071443.GQ4161@awork2.anarazel.de>
Date:	Tue, 8 Apr 2014 09:14:43 +0200
From:	Andres Freund <andres@...quadrant.com>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Robert Haas <robertmhaas@...il.com>,
	Josh Berkus <josh@...iodbs.com>,
	Christoph Lameter <cl@...ux.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

Hi,

On 2014-04-07 23:34:27 +0100, 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.

Unsurprisingly I am in favor of this.

>  Documentation/sysctl/vm.txt | 17 +++++++++--------
>  mm/page_alloc.c             |  2 --
>  2 files changed, 9 insertions(+), 10 deletions(-)

But I think linux/topology.h's comment about RECLAIM_DISTANCE should be
adapted as well.

Thanks,

Andres

-- 
 Andres Freund	                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services
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