Re: [PATCH RFC] mm: Implement balance_dirty_pages() through waiting for flusher thread

[Andrew Morton <akpm@linux-foundation.org>]

On Tue, 22 Jun 2010 09:45:22 +0200 Peter Zijlstra <peterz@infradead.org> wrote:

> On Mon, 2010-06-21 at 23:14 -0700, Andrew Morton wrote:
> > +/*
> > + * Compare counter against given value.
> > + * Return 1 if greater, 0 if equal and -1 if less
> > + */
> > +int percpu_counter_compare(struct percpu_counter *fbc, s64 rhs)
> > +{
> > +       s64     count;
> > +
> > +       count = percpu_counter_read(fbc);
> > +       /* Check to see if rough count will be sufficient for comparison */
> > +       if (abs(count - rhs) > (percpu_counter_batch*num_online_cpus())) {
> > +               if (count > rhs)
> > +                       return 1;
> > +               else
> > +                       return -1;
> > +       }
> > +       /* Need to use precise count */
> > +       count = percpu_counter_sum(fbc);
> > +       if (count > rhs)
> > +               return 1;
> > +       else if (count < rhs)
> > +               return -1;
> > +       else
> > +               return 0;
> > +}
> > +EXPORT_SYMBOL(percpu_counter_compare); 
> 
> That won't quite work as advertised for the bdi stuff since we use a
> custom batch size.

Oh come on, of course it will.  It just needs
__percpu_counter_compare() as I mentioned when merging it.

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