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SubjectRe: [PATCH 11/18] block: add bdi flag to indicate risk of io queue underrun
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On Sun, 2011-09-04 at 09:53 +0800, Wu Fengguang wrote:
> +++ linux-next/mm/page-writeback.c 2011-08-31 14:40:58.000000000 +0800
> @@ -1067,6 +1067,9 @@ static void balance_dirty_pages(struct a
> nr_dirty, bdi_thresh, bdi_dirty,
> start_time);
>
> + if (unlikely(!dirty_exceeded && bdi_async_underrun(bdi)))
> + break;
> +
> dirty_ratelimit = bdi->dirty_ratelimit;
> pos_ratio = bdi_position_ratio(bdi, dirty_thresh,
> background_thresh, nr_dirty,

So dirty_exceeded looks like:


1109 dirty_exceeded = (bdi_dirty > bdi_thresh) ||
1110 (nr_dirty > dirty_thresh);

Would it make sense to write it as:

if (nr_dirty > dirty_thresh ||
(nr_dirty > freerun && bdi_dirty > bdi_thresh))
dirty_exceeded = 1;

So that we don't actually throttle bdi thingies when we're still in the
freerun area?



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