Re: [PATCH 2/5] writeback: dirty position control

Peter Zijlstra
2011-08-08T14:42:00Z

On Mon, 2011-08-08 at 22:11 +0800, Wu Fengguang wrote:
> @@ -538,11 +538,6 @@ static unsigned long bdi_position_ratio(
> goal = thresh - thresh / DIRTY_SCOPE;
> origin = 4 * thresh;
>
> - if (unlikely(origin < limit && dirty > (goal + origin) / 2)) {
> - origin = limit; /* auxiliary control line */
> - goal = (goal + origin) / 2;
> - pos_ratio >>= 1;
> - }
> pos_ratio = origin - dirty;
> pos_ratio <<= BANDWIDTH_CALC_SHIFT;
> do_div(pos_ratio, origin - goal + 1);

So basically, pos_ratio = (4t - d) / (25/8)t, which if I'm not mistaken
comes out at 32/25 - 8d/25t. Which simply doesn't make sense at all.