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

[Peter Zijlstra <peterz@infradead.org>]

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.

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