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

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Message-ID: <20140418154918.GD4523@dhcp22.suse.cz>
Date:	Fri, 18 Apr 2014 17:49:18 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Robert Haas <robertmhaas@...il.com>,
	Josh Berkus <josh@...iodbs.com>,
	Andres Freund <andres@...quadrant.com>,
	Christoph Lameter <cl@...ux.com>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/2] Disable zone_reclaim_mode by default

On Mon 07-04-14 23:34:26, 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.
> 
> Those that require zone_reclaim_mode are likely to be able to detect when
> it needs to be enabled and tune appropriately so lets have a sensible
> default for the bulk of users.
> 
>  Documentation/sysctl/vm.txt | 17 +++++++++--------
>  include/linux/mmzone.h      |  1 -
>  mm/page_alloc.c             | 17 +----------------
>  3 files changed, 10 insertions(+), 25 deletions(-)

Auto-enabling caused so many reports in the past that it is definitely
much better to not be clever and let admins enable zone_reclaim where it
is appropriate instead.

For both patches.
Acked-by: Michal Hocko <mhocko@...e.cz>
-- 
Michal Hocko
SUSE Labs
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