[PATCH] introduce task cgroup v2

[KOSAKI Motohiro]

Hi Paul,

very sorry, late responce.

> > +struct task_cgroup {
> > +       struct cgroup_subsys_state css;
> > +       /*
> > +        * the counter to account for number of thread.
> > +        */
> > +       int max_tasks;
> > +       int nr_tasks;
> > +
> > +       spinlock_t lock;
> > +};
> 
> This looks rather like a res_counter. Can you resuse that rather than
> implementing your own read/write/charge/uncharge routines?

honestly, I used res_counter on early version.
but I got bad performance.
tus, I changed to current implementation.

Of cource, if res_counter become faster, I'll use it.