[PATCH 21/27] mm, vmscan: Only wakeup kswapd once per node for the requested classzone

[Mel Gorman]

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@xxxxxxxxxxxxxxxxxxx>
---
 mm/vmscan.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 0298c0977eac..9a1653fedd88 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3426,6 +3426,7 @@ 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;
@@ -3439,8 +3440,16 @@ 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, 0))
-		return;
+
+	/* Only wake kswapd if all zones are unbalanced */
+	for (z = 0; z <= zone_idx(zone); z++) {
+		zone = pgdat->node_zones + z;
+		if (!populated_zone(zone))
+			continue;
+
+		if (zone_balanced(zone, order, 0, classzone_idx))
+			return;
+	}
 
 	trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, zone_idx(zone), order);
 	wake_up_interruptible(&pgdat->kswapd_wait);
-- 
2.6.4