mm: fix check for reclaimable pages in PF_MEMALLOC reclaim throttling

PF_MEMALLOC direct reclaimers get throttled on a node when the sum of
all free pages in each zone fall below half the min watermark.  During
the summation, we want to exclude zones that don't have reclaimables.
Checking the same pgdat over and over again doesn't make sense.

Fixes: 599d0c954f91 ("mm, vmscan: move LRU lists to node")
Link: http://lkml.kernel.org/r/20170228214007.5621-3-hannes@cmpxchg.org
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Hillf Danton <hillf.zj@alibaba-inc.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Jia He <hejianet@gmail.com>
Cc: Mel Gorman <mgorman@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 667644e53b5c488ffa2c8e8bb90e7d0bc3bd5510..52832bedb2ed9eaacfedd97fbb7146e51755733a 100644 (file)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2835,8 +2835,10 @@ static bool allow_direct_reclaim(pg_data_t *pgdat)
 
        for (i = 0; i <= ZONE_NORMAL; i++) {
                zone = &pgdat->node_zones[i];
-               if (!managed_zone(zone) ||
-                   pgdat_reclaimable_pages(pgdat) == 0)
+               if (!managed_zone(zone))
+                       continue;
+
+               if (!zone_reclaimable_pages(zone))
                        continue;
 
                pfmemalloc_reserve += min_wmark_pages(zone);