On Thu, Jun 23, 2011 at 04:32:27PM +0100, P?draig Brady wrote:
> On 23/06/11 16:24, Mel Gorman wrote:
> >
> > Theory 2 it is then. This is to be applied on top of the patch for
> > theory 1.
> >
> > ==== CUT HERE ====
> > mm: vmscan: Prevent kswapd doing excessive work when classzone is unreclaimable
>
> No joy :(
>
Joy is indeed rapidly fleeing the vicinity.
Check /proc/sys/vm/laptop_mode . If it's set, unset it and try again.
If it's still broken, it's time for theory 3. Still against 2.6.38
and on top of theories 1+2.
==== CUT HERE ====
mm: vmscan: Do not apply pressure to slab if we are not applying pressure to zone
When kswapd applies pressure to zones during node balancing, it checks
if the zone is above a high+balance_gap threshold. If it is, it does
not apply pressure but it unconditionally shrinks slab on a global
basis which is excessive. In the event kswapd is being kept awake due to
a high small unreclaimable zone, it can end up spinning calling
shrink_slab() uselessly.
Once pressure has been applied, the check for zone being unreclaimable
is being made before the check is made if all_unreclaimable should
be set and avoids accounting for scanned in laptop_mode. This miss
of an unreclaimable check can cause has_under_min_watermark_zone to
be set due to an unreclaimable zone preventing kswapd backing off
on congestion_wait().
---
mm/vmscan.c | 27 +++++++++++++++------------
1 files changed, 15 insertions(+), 12 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index dce95dd..c8c0f5a 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2426,19 +2426,19 @@ loop_again:
* zone has way too many pages free already.
*/
if (!zone_watermark_ok_safe(zone, order,
- 8*high_wmark_pages(zone), end_zone, 0))
- shrink_zone(priority, zone, &sc);
- reclaim_state->reclaimed_slab = 0;
- nr_slab = shrink_slab(sc.nr_scanned, GFP_KERNEL,
- lru_pages);
- sc.nr_reclaimed += reclaim_state->reclaimed_slab;
- total_scanned += sc.nr_scanned;
+ 8*high_wmark_pages(zone), end_zone, 0)) {
+ shrink_zone(priority, zone, &sc);
+
+ reclaim_state->reclaimed_slab = 0;
+ nr_slab = shrink_slab(sc.nr_scanned, GFP_KERNEL,
+ lru_pages);
+ sc.nr_reclaimed += reclaim_state->reclaimed_slab;
+ total_scanned += sc.nr_scanned;
+
+ if (nr_slab == 0 && !zone_reclaimable(zone))
+ zone->all_unreclaimable = 1;
+ }
- if (zone->all_unreclaimable)
- continue;
- if (nr_slab == 0 &&
- !zone_reclaimable(zone))
- zone->all_unreclaimable = 1;
/*
* If we've done a decent amount of scanning and
* the reclaim ratio is low, start doing writepage
@@ -2448,6 +2448,9 @@ loop_again:
total_scanned > sc.nr_reclaimed + sc.nr_reclaimed / 2)
sc.may_writepage = 1;
+ if (zone->all_unreclaimable)
+ continue;
+
if (!zone_watermark_ok_safe(zone, order,
high_wmark_pages(zone), end_zone, 0)) {
all_zones_ok = 0;
--
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