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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Date:	Thu, 13 Sep 2012 19:39:58 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Tejun Heo <tj@...nel.org>
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

On Thu 13-09-12 10:18:32, Tejun Heo wrote:
> 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?  

Exactly. 1st level of children under the root is exactly this kind of
setup.

> If so, I have no objection.  Will incorporate your updated version.

Thanks!

-- 
Michal Hocko
SUSE Labs
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