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Date: Mon, 12 Mar 2012 23:31:14 +0100
From: Lennart Poettering <mzxreary@0pointer.de>
To: Tejun Heo <tj@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>, Li Zefan <lizf@cn.fujitsu.com>,
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        Frederic Weisbecker <fweisbec@gmail.com>, linux-kernel@vger.kernel.org,
        Vivek Goyal <vgoyal@redhat.com>, Michal Schmidt <mschmidt@redhat.com>
Subject: Re: [RFD] cgroup: about multiple hierarchies
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On Mon, 12.03.12 15:28, Tejun Heo (tj@kernel.org) wrote:

> 
> Hey,
> 
> On Mon, Mar 12, 2012 at 11:22:18PM +0100, Peter Zijlstra wrote:
> > On Mon, 2012-03-12 at 15:10 -0700, Tejun Heo wrote:
> > > 
> > > * How to map controllers which aren't aware of full hierarchy is still
> > >   an open question but I'm still standing by one active node on any
> > >   root-to-leaf path w/ root group serving as the special rest group. 
> > 
> > What does this mean?
> 
> Let's say we have a tree like the following.
> 
>          root
>       /   |   \
>      G1  G2   G3
>              /  \
> 	   G31  G32
> 
> So, for cgroups which don't support full hierarchy, it'll be viewed as
> either,
> 
>          root
>       /   |   \
>      G1  G2   G3
> 
> or
> 
>           root
>       /   |   |  \
>      G1  G2  G31 G32
> 
> With root being treated specially, probably as just being a equal
> group as other groups, I'm not fully determined about that yet.

Note that at least systemd places all services by default beneath a
single "super" group (/system/), hence the first suggestion would make
little sense for us. The second suggestion would be fine however.

Lennart

-- 
Lennart Poettering - Red Hat, Inc.