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Date: Sun, 11 Dec 2011 14:11:43 -0500
From: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
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To: Glauber Costa <glommer@parallels.com>
CC: Peter Zijlstra <a.p.zijlstra@chello.nl>, Paul Turner <pjt@google.com>,
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        devel@openvz.org, Linux Containers <containers@lists.osdl.org>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
        Balbir Singh <bsingharora@gmail.com>,
        Serge Hallyn <serge.hallyn@canonical.com>,
        Frederic Weisbecker <fweisbec@gmail.com>
Subject: Re: How to draw values for /proc/stat
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>>> IOW a /proc namespace coupled to cgroup scope would do what you want.
>>> Now my head hurts..
>>
>> Mine too. The idea is good, but too broad. Boils down to: How do you
>> couple them? And none of the methods I thought about seemed to make any
>> sense.
>>
>> If we really want to have the values in /proc being opted-in, I think
>> Kamezawa's idea of a mount option is the winner so far.

 > diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
 > index 1b7f9d5..f0bc2e9 100644
 > --- a/include/linux/cgroup.h
 > +++ b/include/linux/cgroup.h
 > @@ -158,6 +158,7 @@ enum {
 > 	 * Clone cgroup values when creating a new child cgroup
 > 	 */
 > 	CGRP_CLONE_CHILDREN,
 > +	CGRP_PROC_OVERLAY,
 > };

I'm not cgroup expert, but I doubt it is mount option. I suspect it's
cgroup option. That's said, if we have following two directories,

/cgroup-for-virtualization
/cgroup-for-resource-management

are both directory affected the overlay flag? I don't think it is not
optimal. Why? we must care some system software (e.g. kvm, systemd) are
using cgroup internally and we expected this trend will grow more.

So, I doubt namespace issue can be solved by such tiny patch.