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

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Message-ID: <50489270.7060108@parallels.com>
Date:	Thu, 6 Sep 2012 16:09:20 +0400
From:	Glauber Costa <glommer@...allels.com>
To:	Michal Hocko <mhocko@...e.cz>
CC:	Tejun Heo <tj@...nel.org>, <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 09/06/2012 04:06 PM, Michal Hocko wrote:
> 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.
> 
Just so I understand it:

Michal clearly objected before folding his patch with my Kconfig patch.
But is there still opposition to merge both?

By having it default-n, only people that are either sure that this is
safe for them, or have more clearly defined lifecycles could set it.

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