On Mon, Dec 05, 2016 at 01:49:55PM +0100, Michal Hocko wrote: > [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. To prevent further confusion, I am dropping these patches from my tree: 80c099e11c19 ("mm: Prevent shrink_node() RCU CPU stall warnings") 34c53f5cd399 ("mm: Prevent shrink_node_memcg() RCU CPU stall warnings") If you need them, please feel free to pull them in. Given that I don't have those, I am dropping this one as well: f2a471ffc8a8 ("rcu: Allow boot-time use of cond_resched_rcu_qs()") If you need it, please let me know. > > 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. And 0day just told me that my current attempt gets a 227% increase in context switches on the unlink tests in LTP, so back to the drawing board... Thanx, Paul -- 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>