mm, page_alloc: wake kswapd based on the highest eligible zone

The ac_classzone_idx is used as the basis for waking kswapd and that is
based on the preferred zoneref.  If the preferred zoneref's first zone
is lower than what is available on other nodes, it's possible that
kswapd is woken on a zone with only higher, but still eligible, zones.
As classzone_idx is strictly adhered to now, it causes a problem because
eligible pages are skipped.

For example, node 0 has only DMA32 and node 1 has only NORMAL.  An
allocating context running on node 0 may wake kswapd on node 1 telling
it to skip all NORMAL pages.

Link: http://lkml.kernel.org/r/1467970510-21195-23-git-send-email-mgorman@techsingularity.net
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: Hillf Danton <hillf.zj@alibaba-inc.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
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>

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index a34d9fcf1339b64fa41fc7b9d2bd3859a1a76aee..f2c56a13b0659ac0131b72c61a24b8cb56147849 100644 (file)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3372,7 +3372,7 @@ static void wake_all_kswapds(unsigned int order, const struct alloc_context *ac)
        for_each_zone_zonelist_nodemask(zone, z, ac->zonelist,
                                        ac->high_zoneidx, ac->nodemask) {
                if (last_pgdat != zone->zone_pgdat)
-                       wakeup_kswapd(zone, order, ac_classzone_idx(ac));
+                       wakeup_kswapd(zone, order, ac->high_zoneidx);
                last_pgdat = zone->zone_pgdat;
        }
 }