From 4f39381a02f87a3702e08d45a7203e039af05281 Mon Sep 17 00:00:00 2001 From: Mel Gorman Date: Fri, 24 Feb 2017 14:59:07 -0800 Subject: [PATCH] mm, vmscan: clear PGDAT_WRITEBACK when zone is balanced commit c2f83143f1c67d186520b72b6cefbf0aa07a34ee upstream. Hillf Danton pointed out that since commit 1d82de618dd ("mm, vmscan: make kswapd reclaim in terms of nodes") that PGDAT_WRITEBACK is no longer cleared. It was not noticed as triggering it requires pages under writeback to cycle twice through the LRU and before kswapd gets stalled. Historically, such issues tended to occur on small machines writing heavily to slow storage such as a USB stick. Once kswapd stalls, direct reclaim stalls may be higher but due to the fact that memory pressure is required, it would not be very noticable. Michal Hocko suggested removing the flag entirely but the conservative fix is to restore the intended PGDAT_WRITEBACK behaviour and clear the flag when a suitable zone is balanced. Fixes: 1d82de618ddd ("mm, vmscan: make kswapd reclaim in terms of nodes") Link: http://lkml.kernel.org/r/20170203203222.gq7hk66yc36lpgtb@suse.de Signed-off-by: Mel Gorman Acked-by: Johannes Weiner Acked-by: Michal Hocko Acked-by: Hillf Danton Cc: Minchan Kim Cc: Rik van Riel Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Amit Pundir Signed-off-by: Greg Kroah-Hartman --- mm/vmscan.c | 1 + 1 file changed, 1 insertion(+) diff --git a/mm/vmscan.c b/mm/vmscan.c index f03ca5ab86b1..cfffef1f26a8 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -3123,6 +3123,7 @@ static bool zone_balanced(struct zone *zone, int order, int classzone_idx) */ clear_bit(PGDAT_CONGESTED, &zone->zone_pgdat->flags); clear_bit(PGDAT_DIRTY, &zone->zone_pgdat->flags); + clear_bit(PGDAT_WRITEBACK, &zone->zone_pgdat->flags); return true; }