linux-kernel - Re: [PATCH REPOST RFC cgroup/for-3.7] cgroup: mark subsystems with broken hierarchy support and whine if cgroups are nested for them

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Message-ID: <20120913171832.GY7677@google.com>
Date:	Thu, 13 Sep 2012 10:18:32 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	Glauber Costa <glommer@...allels.com>,
	linux-kernel@...r.kernel.org,
	containers@...ts.linux-foundation.org, cgroups@...r.kernel.org,
	Li Zefan <lizefan@...wei.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Paul Turner <pjt@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Thomas Graf <tgraf@...g.ch>,
	"Serge E. Hallyn" <serue@...ibm.com>,
	Vivek Goyal <vgoyal@...hat.com>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Neil Horman <nhorman@...driver.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Subject: Re: [PATCH REPOST RFC cgroup/for-3.7] cgroup: mark subsystems with
 broken hierarchy support and whine if cgroups are nested for them

Hello, Michal.

On Thu, Sep 13, 2012 at 02:14:38PM +0200, Michal Hocko wrote:
> I would like to see use_hierarchy go away. The only concern I have is 
> to warn only if somebody is doing something wrong (aka flat
> hierarchies). Or better put it this way. Do not warn in cases which do
> not change if use_hierarchy is gone or default changes to 1.
> An example:
> root (use_hierarchy=0)
>  | \
>  |  A (use_hierarchy=0)
>  |
>  B (use_hierarachy=1)
>  |\
>  C D
> 
> is a perfectly sane configuration and I do not see any reason to fill
> logs with some scary warnings when A is created. There will be no
> semantical change in this setup When use_hierchy is gone.
> 
> So the only thing I am proposing here is to warn only if something
> should be fixed in the configuration in order to be prepared for fully
> hierarchical (and that is a second level of children from root with
> use_hierachy==0).
> 
> Does it make more sense now?

Ah, okay, so what you're saying is that we shouldn't warn if 0
.use_hierarchys don't make any behavior difference from when they're
all 1, right?  If so, I have no objection.  Will incorporate your
updated version.

Thanks.

-- 
tejun
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