Re: [RFD] Merge task counter into memcg

From: Tejun Heo
Date: Tue Apr 17 2012 - 11:41:22 EST


On Fri, Apr 13, 2012 at 10:42:24AM +0900, KAMEZAWA Hiroyuki wrote:
> > So, there's spectrum of solutions between merging task counter and
> > just directing everyone to kmem without distinguishing task resource
> > at all, and at the moment voices in my head are succeeding at making
> > cases for both directions. What do you guys think about the above two
> > issues?
> To be honest, I doubt that task counter is unnecessary...memcg can catch
> oom situation well. I often test 'make -j' under memcg.

Heh, the double negation is confusing me. Were you trying to say that
task_counter is necessary or was it the other way around?

> To the questions
> * It sounds like a 'ulimit' cgroup. How about overwriting
> ulimit values via cgroup ? (sounds joke?) Then, overhead will be small but
> I'm not sure it can be hierarchical and doesn't break userland.
> If people wants to limit the number of tasks, I think interface should provide it
> in the unit of objects. Then, I'm ok to have other subsystem for counting something.
> fork-bomb's memory overhead can be prevent by memcg. What memcg cannot handle
> is ulimit. If forkbomb exhausts all ulimit/tasks, the user cannot login.
> So, having task-limit cgroup subsys for a sandbox will make sense in some situation.
> In short, I don't think it's better to have task-counting and fd-counting in memcg.
> It's kmem, but it's more than that, I think.
> Please provide subsys like ulimit.

So, you think that while kmem would be enough to prevent fork-bombs,
it would still make sense to limit in more traditional ways
(ie. ulimit style object limits). Hmmm....


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