Re: INFO: rcu_sched detected stalls on CPUs/tasks with `kswapd` and `mem_cgroup_shrink_node`

[Boris Zhmurov]

Michal Hocko 30/11/16 21:25:

>>> Do I get it right that s@cond_resched_rcu_qs@cond_resched@ didn't help?
>>
>> I didn't try that. I've tried 4 patches from Paul's linux-rcu tree.
>> I can try another portion of patches, no problem :)
> 
> Replacing cond_resched_rcu_qs in shrink_node_memcg by cond_resched would
> be really helpful to tell whether we are missing a real scheduling point
> or whether something more serious is going on here.

Well, I can confirm, that replacing cond_resched_rcu_qs in
shrink_node_memcg by cond_resched also makes dmesg clean from RCU CPU
stall warnings.

I've attached patch (just modification of Paul's patch), that fixes RCU
stall messages in situations, when all memory is used by
couchbase/memcached + fs cache and linux starts to use swap.


-- 
Boris Zhmurov
System/Network Administrator
mailto: bb@xxxxxxxxxxxxxx
"wget http://kernelpanic.ru/bb_public_key.pgp -O - | gpg --import"
--- a/mm/vmscan.c.orig	2016-11-30 21:52:58.314895320 +0300
+++ b/mm/vmscan.c	2016-11-30 21:53:29.502895320 +0300
@@ -2352,6 +2352,7 @@
 				nr_reclaimed += shrink_list(lru, nr_to_scan,
 							    lruvec, sc);
 			}
+			cond_resched();
 		}
 
 		if (nr_reclaimed < nr_to_reclaim || scan_adjusted)