Re: [PATCH 05/10] writeback: per task dirty rate limit

[Wu Fengguang]

On Fri, Aug 26, 2011 at 08:51:09PM +0800, Peter Zijlstra wrote:
> On Fri, 2011-08-26 at 19:38 +0800, Wu Fengguang wrote:
> > +       preempt_disable();
> >         /*
> > -        * Check the rate limiting. Also, we do not want to throttle real-time
> > -        * tasks in balance_dirty_pages(). Period.
> > +        * This prevents one CPU to accumulate too many dirtied pages without
> > +        * calling into balance_dirty_pages(), which can happen when there are
> > +        * 1000+ tasks, all of them start dirtying pages at exactly the same
> > +        * time, hence all honoured too large initial task->nr_dirtied_pause.
> >          */
> > -       preempt_disable();
> >         p =  &__get_cpu_var(bdp_ratelimits);
> 
> 	p = &get_cpu_var(bdp_ratelimits);

Ah yeah.. I actually followed your suggestion, and then find we'll
eventually do two __get_cpu_var() calls here, one for bdp_ratelimits
and the other for dirty_leaks in a planned patch. So let's keep the
preempt_disable()/preempt_enable().

> > -       *p += nr_pages_dirtied;
> > -       if (unlikely(*p >= ratelimit)) {
> > -               ratelimit = sync_writeback_pages(*p);
> > +       if (unlikely(current->nr_dirtied >= ratelimit))
> >                 *p = 0;
> > -               preempt_enable();
> > -               balance_dirty_pages(mapping, ratelimit);
> > -               return;
> > +       else {
> > +               *p += nr_pages_dirtied;
> > +               if (unlikely(*p >= ratelimit_pages)) {
> > +                       *p = 0;
> > +                       ratelimit = 0;
> > +               }
> >         }
> >         preempt_enable(); 
> 
> 	put_cpu_var(bdp_ratelimits);

ditto.

Thanks,
Fengguang
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