linux-kernel - Re: cgroups(7): documenting cgroups v2 thread mode

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Message-ID: <20180110222913.GH3460072@devbig577.frc2.facebook.com>
Date:   Wed, 10 Jan 2018 14:29:13 -0800
From:   Tejun Heo <tj@...nel.org>
To:     "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
Cc:     Peter Zijlstra <peterz@...radead.org>, cgroups@...r.kernel.org,
        lkml <linux-kernel@...r.kernel.org>,
        linux-man <linux-man@...r.kernel.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Mike Galbraith <efault@....de>, Li Zefan <lizefan@...wei.com>,
        Ingo Molnar <mingo@...hat.com>, Paul Turner <pjt@...gle.com>,
        kernel-team@...com, Andy Lutomirski <luto@...capital.net>,
        Johannes Weiner <hannes@...xchg.org>,
        Lauro Venancio <lvenanci@...hat.com>,
        Waiman Long <longman@...hat.com>
Subject: Re: cgroups(7): documenting cgroups v2 thread mode

Hello,

On Wed, Jan 10, 2018 at 11:18:48PM +0100, Michael Kerrisk (man-pages) wrote:
> Ahh yes. Now I understand. I made the description of the containment
> rules for cgroup.threads more explicit in the text:
> 
>        As with writing to cgroup.procs, some containment rules apply when
>        writing to the cgroup.threads file:
> 
>        *  The  writer  must  have  write permission on the cgroup.threads
>           file in the destination cgroup.
> 
>        *  The writer must have write permission on the cgroup.procs  file
>           in  the  common ancestor of the source and destination cgroups.
>           (In some cases, the common ancestor may be the source or desti‐
>           nation cgroup itself.)
> 
>        *  The source and destination cgroups must be in the same threaded
>           subtree.  (Outside a threaded subtree, an  attempt  to  move  a
>           thread by writing its thread ID to the cgroup.threads in a dif‐
>           ferent domain cgroup fails with the error EOPNOTSUPP.)
> 
> Okay? (I realize that the last bullet point is a rather different way of
> formulating your idea that "the only extra restriction is that the domain
> cgroup must be the same for the source and destination". But I think the
> reformulation is easier to understand, no?)

It looks great to me.  Me explaining that way is mostly from internal
/ conceptual POV.  Yours is definitely more approachable.

Thanks.

-- 
tejun