On Wed, Jun 25, 2014 at 04:35:28PM -0700, Andrew Morton wrote:
> On Wed, 25 Jun 2014 08:58:48 +0100 Mel Gorman <mgorman@xxxxxxx> wrote:
>
> > @@ -325,7 +321,14 @@ static unsigned long zone_dirty_limit(struct zone *zone)
> > */
> > bool zone_dirty_ok(struct zone *zone)
> > {
> > - unsigned long limit = zone_dirty_limit(zone);
> > + unsigned long limit = zone->dirty_limit_cached;
> > + struct task_struct *tsk = current;
> > +
> > + if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
> > + limit = zone_dirty_limit(zone);
> > + zone->dirty_limit_cached = limit;
> > + limit += limit / 4;
> > + }
>
> Could we get a comment in here explaining what we're doing and why
> PF_LESS_THROTTLE and rt_task control whether we do it?
>
/*
* The dirty limits are lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd)
* and real-time tasks to prioritise their allocations.
* PF_LESS_THROTTLE tasks may be cleaning memory and rt tasks may be
* blocking tasks that can clean pages.
*/
That's fairly weak though. It would also seem reasonable to just delete
this check and allow PF_LESS_THROTTLE and rt_tasks to fall into the slow
path if dirty pages are already fairly distributed between zones.
Johannes, any objection to that limit raising logic being deleted?
--
Mel Gorman
SUSE Labs
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