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[PATCH 22/28] mm, vmscan: Only wakeup kswapd once per node for the requested classzone

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kswapd is woken when zones are below the low watermark but the wakeup
decision is not taking the classzone into account.  Now that reclaim is
node-based, it is only required to wake kswapd once per node and only if
all zones are unbalanced for the requested classzone.

Note that one node might be checked multiple times but there is no cheap
way of tracking what nodes have already been visited for zoneslists that
be ordered by either zone or node.

Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
---
 mm/vmscan.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 9f2376ad4ce3..1931e98d2f67 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3423,6 +3423,7 @@ static int kswapd(void *p)
 void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx)
 {
 	pg_data_t *pgdat;
+	int z;
 
 	if (!populated_zone(zone))
 		return;
@@ -3436,8 +3437,16 @@ void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx)
 	pgdat->kswapd_order = max(pgdat->kswapd_order, order);
 	if (!waitqueue_active(&pgdat->kswapd_wait))
 		return;
-	if (zone_balanced(zone, order, 0))
-		return;
+
+	/* Only wake kswapd if all zones are unbalanced */
+	for (z = 0; z <= classzone_idx; z++) {
+		zone = pgdat->node_zones + z;
+		if (!populated_zone(zone))
+			continue;
+
+		if (zone_balanced(zone, order, classzone_idx))
+			return;
+	}
 
 	trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, zone_idx(zone), order);
 	wake_up_interruptible(&pgdat->kswapd_wait);
-- 
2.6.4

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[PATCH 00/28] Move LRU page reclaim from zones to nodes v4 Mel Gorman <mgorman@techsingularity.net> - 2016-04-12 12:30 +0200
  [PATCH 03/28] mm, vmscan: Move lru_lock to the node Mel Gorman <mgorman@techsingularity.net> - 2016-04-12 12:30 +0200
  [PATCH 09/28] mm, vmscan: Simplify the logic deciding whether kswapd sleeps Mel Gorman <mgorman@techsingularity.net> - 2016-04-12 12:30 +0200
  [PATCH 11/28] mm, vmscan: Clear congestion, dirty and need for compaction on a per-node basis Mel Gorman <mgorman@techsingularity.net> - 2016-04-12 12:30 +0200
  [PATCH 27/28] mm: vmstat: Replace __count_zone_vm_events with a zone id equivalent Mel Gorman <mgorman@techsingularity.net> - 2016-04-12 12:50 +0200
  [PATCH 21/28] mm, vmscan: Update classzone_idx if buffer_heads_over_limit Mel Gorman <mgorman@techsingularity.net> - 2016-04-12 12:50 +0200
  [PATCH 24/28] mm, vmscan: Add classzone information to tracepoints Mel Gorman <mgorman@techsingularity.net> - 2016-04-12 12:50 +0200
  [PATCH 28/28] mm: vmstat: Account per-zone stalls and pages skipped during reclaim Mel Gorman <mgorman@techsingularity.net> - 2016-04-12 12:50 +0200
  [PATCH 17/28] mm: Move page mapped accounting to the node Mel Gorman <mgorman@techsingularity.net> - 2016-04-12 12:50 +0200
  [PATCH 26/28] mm: page_alloc: Cache the last node whose dirty limit is reached Mel Gorman <mgorman@techsingularity.net> - 2016-04-12 12:50 +0200
  [PATCH 25/28] mm, page_alloc: Remove fair zone allocation policy Mel Gorman <mgorman@techsingularity.net> - 2016-04-12 12:50 +0200
  [PATCH 14/28] mm, memcg: Move memcg limit enforcement from zones to nodes Mel Gorman <mgorman@techsingularity.net> - 2016-04-12 12:50 +0200
    [PATCH 15/28] mm, workingset: Make working set detection node-aware Mel Gorman <mgorman@techsingularity.net> - 2016-04-12 12:50 +0200
    [PATCH 23/28] mm: Convert zone_reclaim to node_reclaim Mel Gorman <mgorman@techsingularity.net> - 2016-04-12 12:50 +0200
    [PATCH 20/28] mm: Move vmscan writes and file write accounting to the node Mel Gorman <mgorman@techsingularity.net> - 2016-04-12 12:50 +0200
    [PATCH 16/28] mm, page_alloc: Consider dirtyable memory in terms of nodes Mel Gorman <mgorman@techsingularity.net> - 2016-04-12 12:50 +0200
    [PATCH 18/28] mm: Rename NR_ANON_PAGES to NR_ANON_MAPPED Mel Gorman <mgorman@techsingularity.net> - 2016-04-12 12:50 +0200
    [PATCH 22/28] mm, vmscan: Only wakeup kswapd once per node for the requested classzone Mel Gorman <mgorman@techsingularity.net> - 2016-04-12 12:50 +0200
    [PATCH 19/28] mm: Move most file-based accounting to the node Mel Gorman <mgorman@techsingularity.net> - 2016-04-12 12:50 +0200

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