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:	Tue, 11 Sep 2012 10:07:46 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	linux-kernel@...r.kernel.org,
	containers@...ts.linux-foundation.org, cgroups@...r.kernel.org,
	Li Zefan <lizefan@...wei.com>,
	Glauber Costa <glommer@...allels.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 Tue, Sep 11, 2012 at 12:04:33PM +0200, Michal Hocko wrote:
> >  	cgroup_unlock();
> > @@ -4953,6 +4958,7 @@ mem_cgroup_create(struct cgroup *cont)
> >  						&per_cpu(memcg_stock, cpu);
> >  			INIT_WORK(&stock->work, drain_local_stock);
> >  		}
> > +		mem_cgroup_subsys.broken_hierarchy = !memcg->use_hierarchy;
> 
> Hmmm, this will warn even if we have
> root (default use_hierarchy=0)
>  \
>   A (use_hierarchy=1)
>    \
>     B <- here
> 
> which is unfortunate because it will add a noise to a reasonable
> configuration.

I suppose you're talking about having root group not performing any
accounting and/or control?  I suppose such could be a valid use case
(is it really necessary tho?)  but I don't think .use_hierarchy is the
right interface for that.  If it's absolutely necessary, I think it
should be a root-only flag (even if that ends up using the same code
path).  Eventually, we really want to kill .use_hierarchy, or at least
make it to RO 1.  As it's currently defined, it's just way too
confusing.

> >  		hotcpu_notifier(memcg_cpu_hotplug_callback, 0);
> >  	} else {
> >  		parent = mem_cgroup_from_cont(cont->parent);
> > --- a/net/core/netprio_cgroup.c
> > +++ b/net/core/netprio_cgroup.c
> > @@ -330,7 +330,17 @@ struct cgroup_subsys net_prio_subsys = {
> >  	.subsys_id	= net_prio_subsys_id,
> >  #endif
> >  	.base_cftypes	= ss_files,
> > -	.module		= THIS_MODULE
> > +	.module		= THIS_MODULE,
> > +
> > +	/*
> > +	 * net_prio has artificial limit on the number of cgroups and
> > +	 * disallows nesting making it impossible to co-mount it with other
> > +	 * hierarchical subsystems.  Remove the artificially low PRIOIDX_SZ
> > +	 * limit and properly nest configuration such that children follow
> > +	 * their parents' configurations by default and are allowed to
> > +	 * override and remove the following.
> > +	 */
> > +	.broken_hierarchy = trye,
> 
> typo

Heh, I thought I enabled all controllers.  Thanks. :)

-- 
tejun
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