From f7b60926ebc05944f73d93ffaf6690503b796a88 Mon Sep 17 00:00:00 2001
From: Mel Gorman <mgorman@techsingularity.net>
Date: Thu, 28 Jul 2016 15:45:40 -0700
Subject: [PATCH] mm, vmscan: have kswapd only scan based on the highest
requested zone
kswapd checks all eligible zones to see if they need balancing even if
it was woken for a lower zone. This made sense when we reclaimed on a
per-zone basis because we wanted to shrink zones fairly so avoid
age-inversion problems. Ideally this is completely unnecessary when
reclaiming on a per-node basis. In theory, there may still be anomalies
when all requests are for lower zones and very old pages are preserved
in higher zones but this should be the exceptional case.
Link: http://lkml.kernel.org/r/1467970510-21195-7-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>
---
mm/vmscan.c | 7 ++-----
1 file changed, 2 insertions(+), 5 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 766b36bec829b..c6e61dae382bd 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3209,11 +3209,8 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
sc.nr_reclaimed = 0;
- /*
- * Scan in the highmem->dma direction for the highest
- * zone which needs scanning
- */
- for (i = pgdat->nr_zones - 1; i >= 0; i--) {
+ /* Scan from the highest requested zone to dma */
+ for (i = classzone_idx; i >= 0; i--) {
struct zone *zone = pgdat->node_zones + i;
if (!populated_zone(zone))
--
2.30.2