On Wed, May 20, 2015 at 10:22:21PM +0200, Michal Hocko wrote: > On Wed 20-05-15 19:53:02, Oleg Nesterov wrote: > > On 05/20, Michal Hocko wrote: > > > > > > So I assume the leader simply waits for its threads to finish and it > > > stays in the sibling list. __unhash_process seems like it does the final > > > cleanup and unlinks the leader from the lists. Which means that > > > mm_update_next_owner never sees !group_leader. Is that correct Oleg? > > > > Yes, yes, the group leader can't go away until the whole thread-group dies. > > OK, then we should have a guarantee that mm->owner is always thread > group leader, right? > > > But can't we kill mm->owner somehow? > > I would be happy about that. But it is not that simple. > > > I mean, turn it into something else, > > ideally into "struct mem_cgroup *" although I doubt this is possible. > > Sounds like a good idea but... it duplicates the cgroup tracking into > two places and that asks for troubles. On the other hand we are doing > that already because mm->owner might be in a different cgroup than the > current. However, this is an inherent problem because CLONE_VM doesn't > imply CLONE_THREAD. So in the end it doesn't look much worse IMO. > We will loose the "this task is in charge" aspect and that would > be a user space visible change but I am not sure how much it is a > problem. Maybe somebody is (ab)using this to workaround the restriction > that all threads are in the same cgroup. If mm->owner is currently always the threadgroup leader, it should be fairly straight forward to maintain mm->memcg on all events that move any threadgroup leader between cgroups, without having mm->owner, no? It would have a lot of benefits for sure. The code would be simpler, but it would also reduce some of the cost that Mel is observing inside __mem_cgroup_count_vm_event(), by reducing one level of indirection. -- 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>