mm, vmscan: only wakeup kswapd once per node for the requested classzone

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 if the zonelist is
ordered by node because there is no cheap way of tracking what nodes
have already been visited.  For zone-ordering, each node should be
checked only once.

Link: http://lkml.kernel.org/r/1467970510-21195-22-git-send-email-mgorman@techsingularity.net
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Rik van Riel <riel@surriel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 6 insertions, 2 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 0f92e04b58db..a34d9fcf1339 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3367,10 +3367,14 @@ static void wake_all_kswapds(unsigned int order, const struct alloc_context *ac)
 {
         struct zoneref *z;
         struct zone *zone;
+        pg_data_t *last_pgdat = NULL;
 
         for_each_zone_zonelist_nodemask(zone, z, ac->zonelist,
-                                                ac->high_zoneidx, ac->nodemask)
-                wakeup_kswapd(zone, order, ac_classzone_idx(ac));
+                                        ac->high_zoneidx, ac->nodemask) {
+                if (last_pgdat != zone->zone_pgdat)
+                        wakeup_kswapd(zone, order, ac_classzone_idx(ac));
+                last_pgdat = zone->zone_pgdat;
+        }
 }
 
 static inline unsigned int