vmscan: throttle direct reclaim when too many pages are isolated already

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.

Signed-off-by: Rik van Riel <riel@redhat.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 75c29974e878ad67cc14eaf60afd68b41b4cc627..f90b76086ffaa2f9135ed693ba988de7677652cb 100644 (file)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1033,6 +1033,31 @@ int isolate_lru_page(struct page *page)
        return ret;
 }
 
+/*
+ * Are there way too many processes in the direct reclaim path already?
+ */
+static int too_many_isolated(struct zone *zone, int file,
+               struct scan_control *sc)
+{
+       unsigned long inactive, isolated;
+
+       if (current_is_kswapd())
+               return 0;
+
+       if (!scanning_global_lru(sc))
+               return 0;
+
+       if (file) {
+               inactive = zone_page_state(zone, NR_INACTIVE_FILE);
+               isolated = zone_page_state(zone, NR_ISOLATED_FILE);
+       } else {
+               inactive = zone_page_state(zone, NR_INACTIVE_ANON);
+               isolated = zone_page_state(zone, NR_ISOLATED_ANON);
+       }
+
+       return isolated > inactive;
+}
+
 /*
  * shrink_inactive_list() is a helper for shrink_zone().  It returns the number
  * of reclaimed pages
@@ -1048,6 +1073,14 @@ static unsigned long shrink_inactive_list(unsigned long max_scan,
        struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
        int lumpy_reclaim = 0;
 
+       while (unlikely(too_many_isolated(zone, file, sc))) {
+               congestion_wait(WRITE, HZ/10);
+
+               /* We are about to die and free our memory. Return now. */
+               if (fatal_signal_pending(current))
+                       return SWAP_CLUSTER_MAX;
+       }
+
        /*
         * If we need a large contiguous chunk of memory, or have
         * trouble getting a small set of contiguous pages, we