From: Shakeel Butt shakeelb@google.com
commit dffcac2cb88e4ec5906235d64a83d802580b119e upstream.
In production we have noticed hard lockups on large machines running large jobs due to kswaps hoarding lru lock within isolate_lru_pages when sc->reclaim_idx is 0 which is a small zone. The lru was couple hundred GiBs and the condition (page_zonenum(page) > sc->reclaim_idx) in isolate_lru_pages() was basically skipping GiBs of pages while holding the LRU spinlock with interrupt disabled.
On further inspection, it seems like there are two issues:
(1) If kswapd on the return from balance_pgdat() could not sleep (i.e. node is still unbalanced), the classzone_idx is unintentionally set to 0 and the whole reclaim cycle of kswapd will try to reclaim only the lowest and smallest zone while traversing the whole memory.
(2) Fundamentally isolate_lru_pages() is really bad when the allocation has woken kswapd for a smaller zone on a very large machine running very large jobs. It can hoard the LRU spinlock while skipping over 100s of GiBs of pages.
This patch only fixes (1). (2) needs a more fundamental solution. To fix (1), in the kswapd context, if pgdat->kswapd_classzone_idx is invalid use the classzone_idx of the previous kswapd loop otherwise use the one the waker has requested.
Link: http://lkml.kernel.org/r/20190701201847.251028-1-shakeelb@google.com Fixes: e716f2eb24de ("mm, vmscan: prevent kswapd sleeping prematurely due to mismatched classzone_idx") Signed-off-by: Shakeel Butt shakeelb@google.com Reviewed-by: Yang Shi yang.shi@linux.alibaba.com Acked-by: Mel Gorman mgorman@techsingularity.net Cc: Johannes Weiner hannes@cmpxchg.org Cc: Michal Hocko mhocko@suse.com Cc: Vlastimil Babka vbabka@suse.cz Cc: Hillf Danton hdanton@sina.com Cc: Roman Gushchin guro@fb.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- mm/vmscan.c | 27 +++++++++++++++------------ 1 file changed, 15 insertions(+), 12 deletions(-)
--- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -3599,19 +3599,18 @@ out: }
/* - * pgdat->kswapd_classzone_idx is the highest zone index that a recent - * allocation request woke kswapd for. When kswapd has not woken recently, - * the value is MAX_NR_ZONES which is not a valid index. This compares a - * given classzone and returns it or the highest classzone index kswapd - * was recently woke for. + * The pgdat->kswapd_classzone_idx is used to pass the highest zone index to be + * reclaimed by kswapd from the waker. If the value is MAX_NR_ZONES which is not + * a valid index then either kswapd runs for first time or kswapd couldn't sleep + * after previous reclaim attempt (node is still unbalanced). In that case + * return the zone index of the previous kswapd reclaim cycle. */ static enum zone_type kswapd_classzone_idx(pg_data_t *pgdat, - enum zone_type classzone_idx) + enum zone_type prev_classzone_idx) { if (pgdat->kswapd_classzone_idx == MAX_NR_ZONES) - return classzone_idx; - - return max(pgdat->kswapd_classzone_idx, classzone_idx); + return prev_classzone_idx; + return pgdat->kswapd_classzone_idx; }
static void kswapd_try_to_sleep(pg_data_t *pgdat, int alloc_order, int reclaim_order, @@ -3752,7 +3751,7 @@ kswapd_try_sleep:
/* Read the new order and classzone_idx */ alloc_order = reclaim_order = pgdat->kswapd_order; - classzone_idx = kswapd_classzone_idx(pgdat, 0); + classzone_idx = kswapd_classzone_idx(pgdat, classzone_idx); pgdat->kswapd_order = 0; pgdat->kswapd_classzone_idx = MAX_NR_ZONES;
@@ -3806,8 +3805,12 @@ void wakeup_kswapd(struct zone *zone, gf if (!cpuset_zone_allowed(zone, gfp_flags)) return; pgdat = zone->zone_pgdat; - pgdat->kswapd_classzone_idx = kswapd_classzone_idx(pgdat, - classzone_idx); + + if (pgdat->kswapd_classzone_idx == MAX_NR_ZONES) + pgdat->kswapd_classzone_idx = classzone_idx; + else + pgdat->kswapd_classzone_idx = max(pgdat->kswapd_classzone_idx, + classzone_idx); pgdat->kswapd_order = max(pgdat->kswapd_order, order); if (!waitqueue_active(&pgdat->kswapd_wait)) return;