[CC Vlastimil] On Sun 05-02-17 12:46:20, Shantanu Goel wrote: > Hi, > > On 4.9.7 kswapd is failing to wake up kcompactd due to a mismatch in the zone balance check between balance_pgdat() and prepare_kswapd_sleep(). balance_pgdat() returns as soon as a single zone satisfies the allocation but prepare_kswapd_sleep() requires all zones to do the same. This causes prepare_kswapd_sleep() to never succeed except in the order == 0 case and consequently, wakeup_kcompactd() is never called. On my machine prior to apply this patch, the state of compaction from /proc/vmstat looked this way after a day and a half of uptime: > > compact_migrate_scanned 240496 > compact_free_scanned 76238632 > compact_isolated 123472 > compact_stall 1791 > compact_fail 29 > compact_success 1762 > compact_daemon_wake 0 > > > After applying the patch and about 10 hours of uptime the state looks like this: > > compact_migrate_scanned 59927299 > compact_free_scanned 2021075136 > compact_isolated 640926 > compact_stall 4 > compact_fail 2 > compact_success 2 > compact_daemon_wake 5160 > > > Thanks, > Shantanu > From 46f2e4b02ac263bf50d69cdab3bcbd7bcdea7415 Mon Sep 17 00:00:00 2001 > From: Shantanu Goel <sgoel01@xxxxxxxxx> > Date: Sat, 4 Feb 2017 19:07:53 -0500 > Subject: [PATCH] vmscan: fix zone balance check in prepare_kswapd_sleep > > The check in prepare_kswapd_sleep needs to match the one in balance_pgdat > since the latter will return as soon as any one of the zones in the > classzone is above the watermark. This is specially important for > higher order allocations since balance_pgdat will typically reset > the order to zero relying on compaction to create the higher order > pages. Without this patch, prepare_kswapd_sleep fails to wake up > kcompactd since the zone balance check fails. > > Signed-off-by: Shantanu Goel <sgoel01@xxxxxxxxx> > --- > mm/vmscan.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 7682469..11899ff 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -3142,11 +3142,11 @@ static bool prepare_kswapd_sleep(pg_data_t *pgdat, int order, int classzone_idx) > if (!managed_zone(zone)) > continue; > > - if (!zone_balanced(zone, order, classzone_idx)) > - return false; > + if (zone_balanced(zone, order, classzone_idx)) > + return true; > } > > - return true; > + return false; > } > > /* > -- > 2.7.4 > -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
