[PATCH 09/27] 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 <mgorman@xxxxxxxxxxxxxxxxxxx>
Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
---
 mm/vmscan.c | 20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index ce712ca1f696..2dafaa06884b 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2546,14 +2546,6 @@ 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.
  */
@@ -2565,6 +2557,7 @@ static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc,
 	unsigned long nr_soft_reclaimed;
 	unsigned long nr_soft_scanned;
 	gfp_t orig_mask;
+	pg_data_t *last_pgdat = NULL;
 
 	/*
 	 * If the number of buffer_heads in the machine exceeds the maximum
@@ -2589,10 +2582,19 @@ static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc,
 		while (!populated_zone(zone->zone_pgdat->node_zones +
 							classzone_idx)) {
 			classzone_idx--;
-			continue;
 		}
 
 		/*
+		 * 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;
+		last_pgdat = zone->zone_pgdat;
+
+		/*
 		 * Take care memory controller reclaiming has small influence
 		 * to global LRU.
 		 */
-- 
2.6.4