On Thu, 20 Jul 2017 08:56:26 +0200 Michal Hocko <mhocko@xxxxxxxxxx> wrote:
>
> > > --- a/mm/vmscan.c
> > > +++ b/mm/vmscan.c
> > > @@ -1713,9 +1713,15 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
> > > int file = is_file_lru(lru);
> > > struct pglist_data *pgdat = lruvec_pgdat(lruvec);
> > > struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
> > > + bool stalled = false;
> > >
> > > while (unlikely(too_many_isolated(pgdat, file, sc))) {
> > > - congestion_wait(BLK_RW_ASYNC, HZ/10);
> > > + if (stalled)
> > > + return 0;
> > > +
> > > + /* wait a bit for the reclaimer. */
> > > + schedule_timeout_interruptible(HZ/10);
> >
> > a) if this task has signal_pending(), this falls straight through
> > and I suspect the code breaks?
>
> It will not break. It will return to the allocation path more quickly
> but no over-reclaim will happen and it will/should get throttled there.
> So nothing critical.
>
> > b) replacing congestion_wait() with schedule_timeout_interruptible()
> > means this task no longer contributes to load average here and it's
> > a (slightly) user-visible change.
>
> you are right. I am not sure it matters but it might be visible.
>
> > c) msleep_interruptible() is nicer
> >
> > d) IOW, methinks we should be using msleep() here?
>
> OK, I do not have objections. Are you going to squash this in or want a
> separate patch explaining all the above?
I'd prefer to have a comment explaining why interruptible sleep is
being used, because that "what if signal_pending()" case is rather a
red flag.
Is it the case that fall-through-if-signal_pending() is the
*preferred* behaviour? If so, the comment should explain this. If it
isn't the preferred behaviour then using uninterruptible sleep sounds
better to me, if only because it saves us from having to test a rather
tricky and rare case.
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