[PATCH] mm: fix 100% CPU kswapd busyloop on unreclaimable nodes fix

[Johannes Weiner]

Check kswapd failure against the cumulative nr_reclaimed count, not
against the count from the lowest priority iteration.

Suggested-by: Minchan Kim <minchan@xxxxxxxxxx>
Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
---
 mm/vmscan.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index ddcff8a11c1e..b834b2dd4e19 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3179,9 +3179,9 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
 	count_vm_event(PAGEOUTRUN);
 
 	do {
+		unsigned long nr_reclaimed = sc.nr_reclaimed;
 		bool raise_priority = true;
 
-		sc.nr_reclaimed = 0;
 		sc.reclaim_idx = classzone_idx;
 
 		/*
@@ -3271,7 +3271,8 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
 		 * Raise priority if scanning rate is too low or there was no
 		 * progress in reclaiming pages
 		 */
-		if (raise_priority || !sc.nr_reclaimed)
+		nr_reclaimed = sc.nr_reclaimed - nr_reclaimed;
+		if (raise_priority || !nr_reclaimed)
 			sc.priority--;
 	} while (sc.priority >= 1);
 
-- 
2.11.1