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

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Message-ID: <20180110174457.GI3668920@devbig577.frc2.facebook.com>
Date:   Wed, 10 Jan 2018 09:44:57 -0800
From:   Tejun Heo <tj@...nel.org>
To:     Roman Gushchin <guro@...com>
Cc:     "Michael Kerrisk (man-pages)" <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 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.

Thanks.

-- 
tejun