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

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Date:   Wed, 10 Jan 2018 09:39:42 -0800
From:   Tejun Heo <tj@...nel.org>
To:     "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
Cc:     Roman Gushchin <guro@...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

Hello, again.

On Wed, Jan 10, 2018 at 09:33:40AM -0800, Tejun Heo wrote:
> Hello, Michael.
> 
> On Wed, Jan 10, 2018 at 06:31:20PM +0100, Michael Kerrisk (man-pages) wrote:
> > So, I am confused. According to Documentation/cgroup-v2.txt,
> > cgoup.threads is delegated:
> > 
> > [[
> > Model of Delegation
> > ~~~~~~~~~~~~~~~~~~~
> > 
> > A cgroup can be delegated in two ways.  First, to a less privileged
> > user by granting write access of the directory and its "cgroup.procs",
> > "cgroup.threads" and "cgroup.subtree_control" files to the user.
> > Second, if the "nsdelegate" mount option is set, automatically to a
> > cgroup namespace on namespace creation.
> > ]]
> > 
> > So, is that a mistake in that text file?
> 
> Yes, it is.  I probably copy&pasted from an earlier version where we
> were marking threaded domains instead of threaded roots.  Will fix it
> right away.

Jesus christ, sorry.  Roman and the document are right.

* cgroup.type is not delegatble, marking it threaded makes the cgroup
  join the parent's domain.

* cgroup.threads is delegatable, because marking the child cgroups as
  threaded make them join the subtree root, and the threads can be
  dispersed across the parent - the delegated root here - and the
  subtree of the child which is marked threaded.

I'll apply Roman's patch.  Sorry about the confusion.

Thanks.

-- 
tejun