linux-kernel - Re: [PATCH v2] memcg: first step towards hierarchical controller

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Message-ID: <20120906120623.GE22426@dhcp22.suse.cz>
Date:	Thu, 6 Sep 2012 14:06:23 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Tejun Heo <tj@...nel.org>
Cc:	Glauber Costa <glommer@...allels.com>,
	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
	linux-mm@...ck.org, Dave Jones <davej@...hat.com>,
	Ben Hutchings <ben@...adent.org.uk>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Turner <pjt@...gle.com>,
	Lennart Poettering <lennart@...ttering.net>,
	Kay Sievers <kay.sievers@...y.org>,
	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH v2] memcg: first step towards hierarchical controller

On Wed 05-09-12 13:12:38, Tejun Heo wrote:
> Hello, Michal.
> 
> On Wed, Sep 05, 2012 at 04:49:42PM +0200, Michal Hocko wrote:
> > Can we settle on the following 3 steps?
> > 1) warn about "flat" hierarchies (give it X releases) - I will push it
> >    to as many Suse code streams as possible (hope other distributions
> >    could do the same)
> 
> I think I'm just gonna trigger WARN from cgroup core if anyone tries
> to create hierarchy with a controller which doesn't support full
> hierarchy.  WARN_ON_ONCE() at first and then WARN_ON() on each
> creation later on.

How do you find out that a controller is not fully hierarchical? Memory
controller can be both.

> > 2) flip the default on the root cgroup & warn when somebody tries to
> >    change it to 0 (give it another X releases) that the knob will be
> >    removed
> > 3) remove the knob and the whole nonsese
> > 4) revert 3 if somebody really objects
> 
> If we can get to 3, I don't think 4 would be a problem.

Agreed.
-- 
Michal Hocko
SUSE Labs
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