On Fri 15-04-16 10:38:15, Tejun Heo wrote: > Hello, Michal. > > On Fri, Apr 15, 2016 at 09:06:01AM +0200, Michal Hocko wrote: > > Tejun was proposing to do the migration async (move the whole > > mem_cgroup_move_charge into the work item). This would solve the problem > > of course. I haven't checked whether this would be safe but it at least > > sounds doable (albeit far from trivial). It would also be a user visible > > change because the new memcg will not contain the moved charges after we > > return to user space. I think this would be acceptable but if somebody > > Not necessarily. The only thing necessary is flushing the work item > after releasing locks but before returning to user. > cpuset_post_attach_flush() does exactly the same thing. Ahh, ok, didn't know that __cgroup_procs_write is doing something controller specific. Yes then we wouldn't need a generic callback if another code like above would be acceptable. > > really relies on the previous behavior I guess we can solve it with a > > post_move cgroup callback which would be called from a lockless context. > > > > Anyway, before we go that way, can we at least consider the possibility > > of removing the kworker creation dependency on the global rwsem? AFAIU > > this locking was added because of the pid controller. Do we even care > > about something as volatile as kworkers in the pid controller? > > It's not just pid controller and the global percpu locking has lower where else would the locking matter? I have only checked the git history to build my picture so I might be missing something of course. > hotpath overhead. We can try to exclude kworkers out of the locking > but that can get really nasty and there are already attempts to add > cgroup support to workqueue. Will think more about it. For now tho, > do you think making charge moving async would be difficult? Well it certainly is not that trivial because it relies on being exclusive with global context. I will have to look closer of course but I cannot guarantee I will get to it before I get back from LSF. We can certainly discuss that at the conference. Johannes will be there as well. Thanks! -- Michal Hocko SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe cgroups" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
