Re: kernel 2.6.22: what IS the VM doing?

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

Sami Farin wrote:
> On Tue, Sep 04, 2007 at 21:37:35 -0400, Rik van Riel wrote:
> > Is the system trying to evict pages like crazy when your
> > system becomes unusable?
>
> I think so..
>
> > If so, I wonder if kswapd is simply doing the wrong thing
> > and trying to evict data from all zones, simply because the
> > highmem zone is low on free pages...
>
> *shrug*

The attached patch should make sure kswapd does not free an
excessive number of pages in zone_normal just because the
pages in zone_highmem are difficult to free.

It does give kswapd a large margin to continue putting equal
pressure on all zones in normal situations.

Sami, could you try out this patch to see if it helps your
situation?

Signed-off-by: Rik van Riel <riel@redhat.com>

--- linux-2.6.22.noarch/mm/vmscan.c.excessive	2007-09-05 12:19:49.000000000 -0400
+++ linux-2.6.22.noarch/mm/vmscan.c	2007-09-05 12:21:40.000000000 -0400
@@ -1371,7 +1371,13 @@ loop_again:
 			temp_priority[i] = priority;
 			sc.nr_scanned = 0;
 			note_zone_scanning_priority(zone, priority);
-			nr_reclaimed += shrink_zone(priority, zone, &sc);
+			/*
+			 * We put equal pressure on every zone, unless one
+			 * zone has way too many pages free already.
+			 */
+			if (!zone_watermark_ok(zone, order, 8*zone->pages_high,
+						end_zone, 0))
+				nr_reclaimed += shrink_zone(priority, zone, &sc);
 			reclaim_state->reclaimed_slab = 0;
 			nr_slab = shrink_slab(sc.nr_scanned, GFP_KERNEL,
 						lru_pages);