linux-kernel - Re: [RFC] Default child of a cgroup

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Date:	Fri, 1 Feb 2008 07:35:46 -0800
From:	"Paul Menage" <menage@...gle.com>
To:	"Peter Zijlstra" <a.p.zijlstra@...llo.nl>
Cc:	vatsa@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
	"Ingo Molnar" <mingo@...e.hu>, containers@...ts.osdl.org,
	dhaval@...ux.vnet.ibm.com, "Balbir Singh" <balbir@...ibm.com>,
	pj@....com
Subject: Re: [RFC] Default child of a cgroup

On Jan 31, 2008 11:58 PM, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> > Is there a restriction in CFS that stops a given group from
> > simultaneously holding tasks and sub-groups? If so, couldn't we change
> > CFS to make it possible rather than enforcing awkward restrictions on
> > cgroups?
>
> I think it is possible, just way more work than the proposed hack.

Seems to me like the right thing to do though.

>
> > If we really can't change CFS in that way, then an alternative would
> > be similar to Peter's suggestion - make cpu_cgroup_can_attach() fail
> > if the cgroup has children, and make cpu_cgroup_create() fail if the
> > cgroup has any tasks - that way you limit the restriction to just the
> > hierarchy that has CFS attached to it, rather than generically for all
> > cgroups
>
> Agreed.
>

Actually, I realised later that this is impossible - since the root
cgroup will have tasks initially, there'd be no way to create the
first child cgroup in the CFS hierarchy.

Paul
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