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

Rik van Riel
2009-07-16T03:11:25Z

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.

>> @@ -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, and use a normal schedule_timeout
otherwise.

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

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