Re: [RFD] Merge task counter into memcg

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

On Thu, Apr 12, 2012 at 01:34:50PM -0300, Glauber Costa wrote:
> On 04/12/2012 11:55 AM, Frederic Weisbecker wrote:
> >I don't know how the kernel stack is allocated for tasks. Do you mean
> >that we allocate a chunck of it for each new task and we could rely
> >on that?
> >
> More than this: amount of kernel stack is really, really something
> indirect if what you want to track is # of processes. Now, Hannes
> made a fair point in his other e-mail about what is a resource and
> what is not.

I start to consider this option, are there other people interested
in accounting/limiting kernel stack as well?

> 
> >>>  After all, we would only restrict the number of tasks for the
> >>>  resources they require
> >It depends if the kernel stack can have other kind of "consumer".
> >
> It also depends on what you really want to achieve.
> If you want to prevent fork bombs, limiting kernel stack will do just fine.

I want:

a) to prevent the forkbomb from going far enough to DDOS the machine
b) to be able to kill that forkbomb once detected, in one go without race
against concurrent forks.

I think a) can work just fine with kernel stack limiting. I also need
to be notified about the fact we reached the limit. And b) should
be feasible with the help of the cgroup freezer. 

> 
> Is there anything for which you need to know exactly the number of
> processes?

No that's really about prevent/kill forkbomb as far as I'm concerned.