Re: [PATCH RFC 0/9] cgroups: add res_counter_write_u64() API

[Frederic Weisbecker <fweisbec-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

On Thu, Dec 12, 2013 at 04:35:09PM -0500, Dwight Engen wrote:
> Hello,
> 
> I've seen that some sort of fork/task limiter has been proposed and
> discussed several times before. Despite the existance of kmem in memcg, a
> fork limiter is still often asked for by container users. Perhaps this is
> due to current granularity in kmem (ie. stack/struct task not split out from
> other slab allocations) but I believe it is just more natural for users to
> express a limit in terms of tasks.
> 
> So what I've done is updated Frederic Weisbecker's task counter patchset and
> tried to address the concerns that I saw people had raised. This involved
> the following changes:
> 
> - merged into cpuacct controller, as it seems there is a desire not to add
>   new controllers, this controller is already heirarchical, and I feel
>   limiting number of tasks/forks fits best here
> - included a fork_limit similar to the one Max Kellermann posted
>   (https://lkml.org/lkml/2011/2/17/116) which is a use case not addressable
>   with memcg
> - ala memcg kmem, for performance reasons don't account unless limit is set
> - ala memcg, allow usage to roll up to root (prevents warnings on
>   uncharge), but still don't allow setting limits in root
> - changed the interface at fork()/exit(), adding
>   can_fork()/cancel_can_fork() modeled on can_attach(). cgroup_fork()
>   can now return failure to fork().
> - ran Frederics selftests, and added a couple more
> 
> I also wrote a small fork micro benchmark to see how this change affected
> performance. I did 20 runs of 100000 fork/exit/waitpid, and took the
> average. Times are in seconds, base is without the change, cpuacct1 is with
> the change but no accounting be done (ie. no limit set), and cpuacct2 is
> with the test being in a cgroup 1 level deep.
> 
> base  cpuacct1  cpuaac2
> 5.59  5.59      5.64
> 
> So I believe this change has minimal performance impact, especially when no
> limit is set.

Sorry for the late answer on this. I'm adding cgroup mailing list and a few
cgroups/kmem people in Cc.

This patchset was eventually abandoned because kmem became the prefered way to
limit the number of tasks that can be forked.

Have you tried it?

Thanks.