linux-kernel - Re: [RFC] cgroup TODOs

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Date:	Fri, 14 Sep 2012 11:53:24 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	containers@...ts.linux-foundation.org, cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org, Li Zefan <lizefan@...wei.com>,
	Michal Hocko <mhocko@...e.cz>,
	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>, 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>,
	Serge Hallyn <serge.hallyn@...ntu.com>
Subject: Re: [RFC] cgroup TODOs

Hello, Vivek.

On Fri, Sep 14, 2012 at 02:07:54PM -0400, Vivek Goyal wrote:
> I am curious that why are you planning to provide capability of controller
> specific view of hierarchy. To me it sounds pretty close to having
> separate hierarchies per controller. Just that it is a little more
> restricted configuration. 

I think it's a lot less crazy and gives us a way to bind a resource to
a set of controller cgroups regardless which task is looking at it,
which is something we're sorely missing now.

> IOW, who is is the user of this functionality and who is asking for it.
> Can we go all out where all controllers have only one hierarchy view.

I think the issue is that controllers inherently have overhead and
behavior alterations depending on the tree organization.  At least
from the usage I see from google which uses nested cgroups
extensively, at least that level of flexibility seems necessary.

In addition, for some resources, granularity beyond certain point
simply doesn't work.  Per-service granularity might make sense for cpu
but applying it by default would be silly for blkio.

Thanks.

-- 
tejun
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