[PATCH 10/34] mm, vmscan: by default have direct reclaim only shrink once per node

[Mel Gorman]

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.

Signed-off-by: Mel Gorman <mgor...@techsingularity.net>
Acked-by: Johannes Weiner <han...@cmpxchg.org>
Acked-by: Vlastimil Babka <vba...@suse.cz>
---
 mm/vmscan.c | 22 ++++++++++++++--------
 1 file 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);
        }
 
-- 
2.6.4