From: Mel Gorman Date: Fri, 24 Feb 2017 22:59:07 +0000 (-0800) Subject: mm, vmscan: clear PGDAT_WRITEBACK when zone is balanced X-Git-Tag: Ubuntu-5.2.0-15.16~7371^2~53 X-Git-Url: https://git.proxmox.com/?a=commitdiff_plain;h=c2f83143f1c67d186520b72b6cefbf0aa07a34ee;p=mirror_ubuntu-eoan-kernel.git mm, vmscan: clear PGDAT_WRITEBACK when zone is balanced 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 --- diff --git a/mm/vmscan.c b/mm/vmscan.c index ae3d982216b5..70aa739c6b68 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -3096,6 +3096,7 @@ 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; }