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

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Message-ID: <20150610045304.GJ11955@mtj.duckdns.org>
Date:	Wed, 10 Jun 2015 13:53:04 +0900
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 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.

Thanks.

-- 
tejun
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