4.9-stable review patch. If anyone has any objections, please let me know.
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From: Mel Gorman mgorman@suse.de
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 mgorman@suse.de Acked-by: Johannes Weiner hannes@cmpxchg.org Acked-by: Michal Hocko mhocko@suse.com Acked-by: Hillf Danton hillf.zj@alibaba-inc.com Cc: Minchan Kim minchan.kim@gmail.com Cc: Rik van Riel riel@redhat.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Amit Pundir amit.pundir@linaro.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- mm/vmscan.c | 1 + 1 file changed, 1 insertion(+)
--- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -3123,6 +3123,7 @@ static bool zone_balanced(struct zone *z */ 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; }