On Mon 21-11-16 06:01:22, Paul E. McKenney wrote: > On Mon, Nov 21, 2016 at 02:41:31PM +0100, Michal Hocko wrote: [...] > > To the patch. I cannot say I would like it. cond_resched_rcu_qs sounds > > way too lowlevel for this usage. If anything cond_resched somewhere inside > > mem_cgroup_iter would be more appropriate to me. > > Like this? > > Thanx, Paul > > ------------------------------------------------------------------------ > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index ae052b5e3315..81cb30d5b2fc 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -867,6 +867,7 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup > *root, > out: > if (prev && prev != root) > css_put(&prev->css); > + cond_resched_rcu_qs();
I still do not understand why should we play with _rcu_qs at all and a regular cond_resched is not sufficient. Anyway I would have to double check whether we can do cond_resched in the iterator. I do not remember having users which are atomic but I might be easily wrong here. Before we touch this code, though, I would really like to understand what is actually going on here because as I've already pointed out we should have some resched points in the reclaim path. -- Michal Hocko SUSE Labs
