linux-kernel - Re: cgroups(7): documenting /sys/kernel/cgroup files

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Message-ID: <16c30b5d-d2c6-ffb0-9374-f48cb3bc154a@gmail.com>
Date:   Wed, 10 Jan 2018 20:14:20 +0100
From:   "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To:     Tejun Heo <tj@...nel.org>, Roman Gushchin <guro@...com>
Cc:     mtk.manpages@...il.com, "Serge E. Hallyn" <serge@...lyn.com>,
        linux-man <linux-man@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        "open list:CONTROL GROUP (CGROUP)" <cgroups@...r.kernel.org>
Subject: Re: cgroups(7): documenting /sys/kernel/cgroup files

On 01/10/2018 06:44 PM, Tejun Heo wrote:
> On Wed, Jan 10, 2018 at 06:02:39AM -0800, Tejun Heo wrote:
>> Hello,
>>
>> On Wed, Jan 10, 2018 at 04:44:14AM -0800, Roman Gushchin wrote:
>>> cgroup.threads is not listed because it's not delegatable (doesn't have
>>> CFTYPE_NS_DELEGATABLE flag set). I don't know if it was intended or just
>>> an accident (I believe the latter).
>>
>> So, thread mode isn't delegatble.  Marking a cgroup as threaded turns
>> that subtree threaded and join the parent's domain, so we can't allow
>> delegation roots to be turned threaded - just like we can't mark the
>> root cgroup threaded, and I'm not really not sure what it means to
>> delegate a portion of threaded subtree.
> 
> Please disregard.
> 
> Just like we can't mark the root cgroup threaded, we can't mark
> delegated subtree root's threaded, so cgroup.type is not delegatable.
> 
> However, the delegated root's children can definitely be marked
> threadaed and they will join the delegated root's domain and the
> threads are free to move between root and the threaded subtree.

Exactly, so cgroup.threads in the threaded root must be made
writable by the delegatee.

Thanks, Tejun.

Cheers,

Michael

-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/