linux-kernel - Re: [RFC] cgroup TODOs

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Message-ID: <20120914203925.GR17747@google.com>
Date:	Fri, 14 Sep 2012 13:39:25 -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, again.

On Fri, Sep 14, 2012 at 12:49:50PM -0700, Tejun Heo wrote:
> That said, if someone can think of a better solution, I'm all ears.
> One thing that *has* to be maintained is that it should be able to tag
> a resource in such way that its associated controllers are
> identifiable regardless of which task is looking at it.

So, I thought about it more.  How about we do "consider / ignore this
node" instead of "(don't) nest beyond this level".  For example, let's
assume a tree like the following.

        R
     /  |  \
    A   B   C
   / \
  AA AB

If we want to differentiate between AA and AB, we'll have to consider
the whole tree with the previous sheme - A needs to nest, so R needs
to nest and we end up with the whole tree.  Instead, if we have honor
/ ignore this node.  We can set the honor bit on A, AA and AB and see
the tree as

        R
     /
    A
   / \
  AA AB

We still see the intermediate A node but can ignore the other
branches.  Implementation and concept-wise, it's fairly simple too.
For any given node and controller, you travel upwards until you meet a
node which has the controller enabled and that's the cgroup the
controller considers.

Thanks.

-- 
tejun
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