Re: [PATCH -mm] throttle direct reclaim when too many pages are isolated already

Andrew Morton
2009-07-16T03:21:36Z

On Wed, 15 Jul 2009 23:10:43 -0400 Rik van Riel <riel@redhat.com> wrote:

> Andrew Morton wrote:
> > On Wed, 15 Jul 2009 22:38:53 -0400 Rik van Riel <riel@redhat.com> wrote:
> >
> >> When way too many processes go into direct reclaim, it is possible
> >> for all of the pages to be taken off the LRU. One result of this
> >> is that the next process in the page reclaim code thinks there are
> >> no reclaimable pages left and triggers an out of memory kill.
> >>
> >> One solution to this problem is to never let so many processes into
> >> the page reclaim path that the entire LRU is emptied. Limiting the
> >> system to only having half of each inactive list isolated for
> >> reclaim should be safe.
> >>
> >
> > Since when? Linux page reclaim has a bilion machine years testing and
> > now stuff like this turns up. Did we break it or is this a
> > never-before-discovered workload?
>
> It's been there for years, in various forms. It hardly ever
> shows up, but Kosaki's patch series give us a nice chance to
> fix it for good.

OK.

> >> @@ -1049,6 +1070,10 @@ static unsigned long shrink_inactive_lis
> >> struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
> >> int lumpy_reclaim = 0;
> >>
> >> + while (unlikely(too_many_isolated(zone, file))) {
> >> + schedule_timeout_interruptible(HZ/10);
> >> + }
> >
> > This (incorrectly-laid-out) code is a no-op if signal_pending().
>
> Good point, I should add some code to break out of page reclaim
> if a fatal signal is pending,

We can't just return NULL from __alloc_pages(), and if we can't
get a page from the freelists then we're just going to have to keep
reclaiming. So I'm not sure how we can do this.

> and use a normal schedule_timeout
> otherwise.

congestion_wait() would be typical.

> Btw, how is this laid out wrong? How do I do this better?

ask checkpatch ;)

WARNING: braces {} are not necessary for single statement blocks
#99: FILE: mm/vmscan.c:1073:
+ while (unlikely(too_many_isolated(zone, file))) {
+ schedule_timeout_interruptible(HZ/10);
+ }

total: 0 errors, 1 warnings, 37 lines checked