Re: [PATCH 10/18] writeback: dirty position control - bdi reservearea

[Peter Zijlstra]

On Wed, 2011-09-07 at 20:31 +0800, Wu Fengguang wrote:
> > > +   x_intercept = min(write_bw, freerun);
> > > +   if (bdi_dirty < x_intercept) {
> > 
> > So the point of the freerun point is that we never throttle before it,
> > so basically all the below shouldn't be needed at all, right? 
> 
> Yes!
> 
> > > +           if (bdi_dirty > x_intercept / 8) {
> > > +                   pos_ratio *= x_intercept;
> > > +                   do_div(pos_ratio, bdi_dirty);
> > > +           } else
> > > +                   pos_ratio *= 8;
> > > +   }
> > > +
> > >     return pos_ratio;
> > >  }

Does that mean we can remove this whole block?

> > 
> > So why not add:
> > 
> >       if (likely(dirty < freerun))
> >               return 2;
> > 
> > at the start of this function and leave it at that?
> 
> Because we already has
> 
>         if (nr_dirty < freerun)
>                 break;
> 
> in the main balance_dirty_pages() loop ;)

Bah! I keep missing that ;-)
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