[CC Paul - sorry I've tried to save you from more emails...] On Mon 05-12-16 23:44:27, Balbir Singh wrote: > > > > Hi, > > there were multiple reportes of the similar RCU stalls. Only Boris has > > confirmed that this patch helps in his workload. Others might see a > > slightly different issue and that should be investigated if it is the > > case. As pointed out by Paul [1] cond_resched might be not sufficient > > to silence RCU stalls because that would require a real scheduling. > > This is a separate problem, though, and Paul is working with Peter [2] > > to resolve it. > > > > Anyway, I believe that this patch should be a good start because it > > really seems that nr_taken=0 during the LRU isolation can be triggered > > in the real life. All reporters are agreeing to start seeing this issue > > when moving on to 4.8 kernel which might be just a coincidence or a > > different behavior of some subsystem. Well, MM has moved from zone to > > node reclaim but I couldn't have found any direct relation to that > > change. > > > > [1] http://lkml.kernel.org/r/20161130142955.GS3924@xxxxxxxxxxxxxxxxxx > > [2] http://lkml.kernel.org/r/20161201124024.GB3924@xxxxxxxxxxxxxxxxxx > > > > mm/vmscan.c | 2 ++ > > 1 file changed, 2 insertions(+) > > > > diff --git a/mm/vmscan.c b/mm/vmscan.c > > index c05f00042430..c4abf08861d2 100644 > > --- a/mm/vmscan.c > > +++ b/mm/vmscan.c > > @@ -2362,6 +2362,8 @@ static void shrink_node_memcg(struct pglist_data *pgdat, struct mem_cgroup *memc > > } > > } > > > > + cond_resched(); > > + > > I see a cond_resched_rcu_qs() as a part of linux next inside the while > (nr[..]) loop. This is a left over from Paul's initial attempt to fix this issue. I expect him to drop his patch from his tree. He has considered it experimental anyway. > Do we need this as well? Paul is working with Peter to make cond_resched general and cover RCU stalls even when cond_resched doesn't schedule because there is no runnable task. -- 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>