linux-kernel - Re: [PATCHSET] kernfs, cgroup: reimplement "cgroup.procs" reading for v2

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Date:   Tue, 27 Dec 2016 14:53:54 -0500
From:   Tejun Heo <tj@...nel.org>
To:     gregkh@...uxfoundation.org, lizefan@...wei.com, hannes@...xchg.org
Cc:     linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
        kernel-team@...com
Subject: Re: [PATCHSET] kernfs, cgroup: reimplement "cgroup.procs" reading
 for v2

On Tue, Dec 20, 2016 at 11:12:17AM -0500, Tejun Heo wrote:
> On cgroup v1, the pid listings in "cgroup.procs" and "tasks" are
> sorted which adds a lot of complications and overhead.  v2 doesn't
> have such requirement and has been intentionally using a modified
> sorting order so that the output doesn't look sorted to users.
> 
> This patchset re-implements "cgroup.procs" reading for v2 which simply
> keeps a css_task_iter open while the file is being read.  Keeping the
> iterator open makes it unnecessary to skip to the right position on
> each read segment and associated errors - e.g. incorrectly skipping
> over pids because earlier pids disappeared between the reads.
> 
> Using persistent iterator across multiple read calls requires
> ->release() callback to clean it up.  kernfs operations
> ->open/release() are added and piped through cftype.

Applied to cgroup/for-4.11.

-- 
tejun