Re: [PATCH 05/10] Make total_forks per-cgroup

[Glauber Costa]

On 10/12/2011 03:45 AM, Frederic Weisbecker wrote:
> On Wed, Oct 05, 2011 at 04:12:00PM +0400, Glauber Costa wrote:
> > On 10/05/2011 01:05 PM, Peter Zijlstra wrote:
> > > On Sun, 2011-10-02 at 23:21 +0400, Glauber Costa wrote:
> > > > This patch counts the total number of forks per-cgroup.
> > > > The information is propagated to the parent, so the total
> > > > number of forks in the system, is the parent cgroup's one.
> > > >
> > > > To achieve that, total_forks is made per-cpu. There is no
> > > > particular reason to do that, but by doing this, we are
> > > > able to bundle it inside the cpustat structure already
> > > > present.
> > >
> > > I think fweisbec is also doing something with forks and cgroups.
> >
> > I am all ears...
> >
> > Frederic, does it conflict with what you're doing ?
>
> I don't know if that really conflicts but I'm working
> on a cgroup subsystem that is able to control the number
> of tasks running in a subsystem.
>
> It consists in two new files added:
>
> * tasks.usage
> * tasks.limit
>
> The subsystem rejects any new fork or migration into the
> cgroup when tasks.usage>  tasks.limit
>
> So tasks.usage can inform you about the number of tasks
> running into the cgroup. It's not strictly the number
> of forks because it also counts the tasks that have been
> attached to the cgroup.
>
> But something like a tasks.fork file could be implemented
> in that subsystem as well.
>
> It depends on what you need.

So the specific piece I am working on, is to display /proc/stat 
information per-cgroup. One of the many fields it has, is total_forks.
(it is actually just a small part of the series)
So instead of tracking how many forks the system has in total, I'll
track it per-cpucgroup.

So I don't think we conflict at all. At the very least, IIUC, you are 
planning to account and check *before* a fork happens, right? This 
particular stat is incremented after it already succeeded.
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