linux-kernel - Re: [PATCH v14 4/4] cgroup: implement the PIDs subsystem

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Date:	Tue, 14 Jul 2015 17:31:48 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Aleksa Sarai <cyphar@...har.com>
Cc:	lizefan@...wei.com, mingo@...hat.com, peterz@...radead.org,
	richard@....at, fweisbec@...il.com, linux-kernel@...r.kernel.org,
	cgroups@...r.kernel.org
Subject: Re: [PATCH v14 4/4] cgroup: implement the PIDs subsystem

On Wed, Jun 10, 2015 at 01:53:04PM +0900, Tejun Heo wrote:
> On Tue, Jun 09, 2015 at 09:32:10PM +1000, Aleksa Sarai wrote:
> > Adds a new single-purpose PIDs subsystem to limit the number of
> > tasks that can be forked inside a cgroup. Essentially this is an
> > implementation of RLIMIT_NPROC that applies to a cgroup rather than a
> > process tree.
> > 
> > However, it should be noted that organisational operations (adding and
> > removing tasks from a PIDs hierarchy) will *not* be prevented. Rather,
> > the number of tasks in the hierarchy cannot exceed the limit through
> > forking. This is due to the fact that, in the unified hierarchy, attach
> > cannot fail (and it is not possible for a task to overcome its PIDs
> > cgroup policy limit by attaching to a child cgroup -- even if migrating
> > mid-fork it must be able to fork in the parent first).
> > 
> > PIDs are fundamentally a global resource, and it is possible to reach
> > PID exhaustion inside a cgroup without hitting any reasonable kmemcg
> > policy. Once you've hit PID exhaustion, you're only in a marginally
> > better state than OOM. This subsystem allows PID exhaustion inside a
> > cgroup to be prevented.
> 
> Patches 3-4 look good to me.  Will apply once v4.3 dev window opens.

Applied 3-4 to cgroup/for-4.3.

Thanks.

-- 
tejun
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