Date: Tue, 8 Apr 2014 09:14:43 +0200
From: Andres Freund <andres@2ndquadrant.com>
To: Mel Gorman <mgorman@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>,
        Robert Haas <robertmhaas@gmail.com>, Josh Berkus <josh@agliodbs.com>,
        Christoph Lameter <cl@linux.com>, Linux-MM <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/2] mm: Disable zone_reclaim_mode by default
Message-ID: <20140408071443.GQ4161@awork2.anarazel.de>
References: <1396910068-11637-1-git-send-email-mgorman@suse.de>
 <1396910068-11637-2-git-send-email-mgorman@suse.de>
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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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