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

[Peter Zijlstra]

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. 


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