On Fri 12-07-13 17:54:27, Li Zefan wrote: > On 2013/7/12 17:29, Michal Hocko wrote: > > On Fri 12-07-13 17:20:09, Li Zefan wrote: > > [...] > >> But if I read the code correctly, even no one registers a vmpressure event, > >> vmpressure() is always running and queue the work item. > > > > True but checking there is somebody is rather impractical. First we > > would have to take a events_lock to check this and then drop it after > > scheduling the work. Which doesn't guarantee that the registered event > > wouldn't go away. > > And even trickier, we would have to do the same for all parents up the > > hierarchy. > > > > The thing is, we can forget about eventfd. eventfd is checked in > vmpressure_work_fn(), while vmpressure() is always called no matter what. But vmpressure is called only for an existing memcg. This means that it cannot be called past css_offline so it must happen _before_ cgroup eventfd cleanup code. Or am I missing something? > vmpressure() > queue_work() > cgroup_diput() > call_rcu(cgroup_free_rcu) > ... > queue_work(destroy_cgroup) > ... > cgroup_free_fn() > mem_cgroup_destroy() > ... > vmpress_work_fn() > > There's no guarantee that vmpressure work is run before cgroup destroy > work, I think. > -- 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>