linux-kernel - Re: [PATCH 2/2] mm, memcg: Optionally disable memcg by default using Kconfig

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Date:	Wed, 20 May 2015 17:44:19 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	Michal Hocko <mhocko@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tejun Heo <tj@...nel.org>,
	Linux-CGroups <cgroups@...r.kernel.org>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] mm, memcg: Optionally disable memcg by default using
 Kconfig

On Wed, May 20, 2015 at 12:24:21PM -0400, Johannes Weiner wrote:
> > 
> > Low thread counts get a small boost but it's within noise as memcg overhead
> > does not dominate. It's not obvious at all at higher thread counts as other
> > factors cause more problems. The overall breakdown of CPU usage looks like
> > 
> >                4.0.0       4.0.0
> >         chargefirst-v2r1disable-v2r1
> > User           41.81       41.45
> > System        407.64      405.50
> > Elapsed       128.17      127.06
> 
> This is a worst case microbenchmark doing nothing but anonymous page
> faults (with THP disabled), and yet the performance difference is in
> the noise.  I don't see why we should burden the user with making a
> decision that doesn't matter in theory, let alone in practice.
> 
> We have CONFIG_MEMCG and cgroup_disable=memory, that should be plenty
> for users that obsess about fluctuation in the noise.  There is no
> reason to complicate the world further for everybody else.

FWIW, I agree and only included this patch because I said I would
yesterday. After patch 1, there is almost no motivation to disable memcg
at all let alone by default.

-- 
Mel Gorman
SUSE Labs
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