mm, vmscan: by default have direct reclaim only shrink once per node

Direct reclaim iterates over all zones in the zonelist and shrinking
them but this is in conflict with node-based reclaim.  In the default
case, only shrink once per node.

Link: http://lkml.kernel.org/r/1467970510-21195-11-git-send-email-mgorman@techsingularity.net
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Rik van Riel <riel@surriel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 14 insertions, 8 deletions

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 905c60473126..01fe4708e404 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2552,14 +2552,6 @@ static inline bool compaction_ready(struct zone *zone, int order, int classzone_
  * try to reclaim pages from zones which will satisfy the caller's allocation
  * request.
  *
- * We reclaim from a zone even if that zone is over high_wmark_pages(zone).
- * Because:
- * a) The caller may be trying to free *extra* pages to satisfy a higher-order
- *    allocation or
- * b) The target zone may be at high_wmark_pages(zone) but the lower zones
- *    must go *over* high_wmark_pages(zone) to satisfy the `incremental min'
- *    zone defense algorithm.
- *
  * If a zone is deemed to be full of pinned pages then just give it a light
  * scan then give up on it.
  */
@@ -2571,6 +2563,7 @@ static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
         unsigned long nr_soft_scanned;
         gfp_t orig_mask;
         enum zone_type classzone_idx;
+        pg_data_t *last_pgdat = NULL;
 
         /*
          * If the number of buffer_heads in the machine exceeds the maximum
@@ -2630,6 +2623,15 @@ static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
                         }
 
                         /*
+                         * Shrink each node in the zonelist once. If the
+                         * zonelist is ordered by zone (not the default) then a
+                         * node may be shrunk multiple times but in that case
+                         * the user prefers lower zones being preserved.
+                         */
+                        if (zone->zone_pgdat == last_pgdat)
+                                continue;
+
+                        /*
                          * This steals pages from memory cgroups over softlimit
                          * and returns the number of reclaimed pages and
                          * scanned pages. This works for global memory pressure
@@ -2644,6 +2646,10 @@ static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
                         /* need some check for avoid more shrink_zone() */
                 }
 
+                /* See comment about same check for global reclaim above */
+                if (zone->zone_pgdat == last_pgdat)
+                        continue;
+                last_pgdat = zone->zone_pgdat;
                 shrink_node(zone->zone_pgdat, sc, classzone_idx);
         }