[PATCH 22/34] mm, page_alloc: wake kswapd based on the highest eligible zone

[Mel Gorman]

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.

Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Acked-by: Hillf Danton <hillf.zj@xxxxxxxxxxxxxxx>
---
 mm/page_alloc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index bb261885c121..e6ee52f1c15f 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3415,7 +3415,7 @@ 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;
 	}
 }
-- 
2.6.4