Re: [PATCH 3/5] writeback: dirty rate control

Peter Zijlstra
2011-08-10T17:10:59Z

On Wed, 2011-08-10 at 22:00 +0800, Wu Fengguang wrote:
>
> > Although I'm not quite sure how he keeps fairness in light of the
> > sleep time bounding to MAX_PAUSE.
>
> Firstly, MAX_PAUSE will only be applied when the dirty pages rush
> high (dirty exceeded). Secondly, the dirty exceeded state is global
> to all tasks, in which case each task will sleep for MAX_PAUSE equally.
> So the fairness is still maintained in dirty exceeded state.

Its not immediately apparent how dirty_exceeded and MAX_PAUSE interact,
but having everybody sleep MAX_PAUSE doesn't necessarily mean its fair,
its only fair if they dirty at the same rate.