Re: [RFC PATCH 1/2] vmscan don't isolate too many pages

[Rik van Riel <riel@redhat.com>]

KOSAKI Motohiro wrote:

> FAQ
> -------
> Q: Why do you compared zone accumulate pages, not individual zone pages?
> A: If we check individual zone, #-of-reclaimer is restricted by smallest zone.
>    it mean decreasing the performance of the system having small dma zone.

That is a clever solution!  I was playing around a bit with
doing it on a per-zone basis.  Your idea is much nicer.

However, I can see one potential problem with your patch:

+		nr_inactive += zone_page_state(zone, NR_INACTIVE_ANON);
+		nr_inactive += zone_page_state(zone, NR_INACTIVE_FILE);
+		nr_isolated += zone_page_state(zone, NR_ISOLATED_ANON);
+		nr_isolated += zone_page_state(zone, NR_ISOLATED_FILE);
+	}
+
+	return nr_isolated > nr_inactive;

What if we ran out of swap space, or are not scanning the
anon list at all for some reason?

It is possible that there are no inactive_file pages left,
with all file pages already isolated, and your function
still letting reclaimers through.

This means you could still get a spurious OOM.

I guess I should mail out my (ugly) approach, so we can
compare the two :)