[PATCH] oom: reclaim_mapped on oom

Potentially it takes several scans of the lru lists before we can even start
reclaiming pages.

mapped pages, with young ptes can take 2 passes on the active list + one on
the inactive list.  But reclaim_mapped may not always kick in instantly, so it
could take even more than that.

Raise the threshold for marking a zone as all_unreclaimable from a factor of 4
time the pages in the zone to 6.  Introduce a mechanism to force
reclaim_mapped if we've reached a factor 3 and still haven't made progress.

Previously, a customer doing stress testing was able to easily OOM the box
after using only a small fraction of its swap (~100MB).  After the patches, it
would only OOM after having used up all swap (~800MB).

Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 10 insertions, 1 deletions

diff --git a/mm/vmscan.c b/mm/vmscan.c
index ba18d0c36b83..8f35d7d585cb 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -697,6 +697,11 @@ done:
         return nr_reclaimed;
 }
 
+static inline int zone_is_near_oom(struct zone *zone)
+{
+        return zone->pages_scanned >= (zone->nr_active + zone->nr_inactive)*3;
+}
+
 /*
  * This moves pages from the active list to the inactive list.
  *
@@ -732,6 +737,9 @@ static void shrink_active_list(unsigned long nr_pages, struct zone *zone,
                 long distress;
                 long swap_tendency;
 
+                if (zone_is_near_oom(zone))
+                        goto force_reclaim_mapped;
+
                 /*
                  * `distress' is a measure of how much trouble we're having
                  * reclaiming pages.  0 -> no problems.  100 -> great trouble.
@@ -767,6 +775,7 @@ static void shrink_active_list(unsigned long nr_pages, struct zone *zone,
                  * memory onto the inactive list.
                  */
                 if (swap_tendency >= 100)
+force_reclaim_mapped:
                         reclaim_mapped = 1;
         }
 
@@ -1161,7 +1170,7 @@ scan:
                         if (zone->all_unreclaimable)
                                 continue;
                         if (nr_slab == 0 && zone->pages_scanned >=
-                                    (zone->nr_active + zone->nr_inactive) * 4)
+                                    (zone->nr_active + zone->nr_inactive) * 6)
                                 zone->all_unreclaimable = 1;
                         /*
                          * If we've done a decent amount of scanning and