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SubjectRe: [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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