Hello, Johannes, Michal. On Tue, May 26, 2015 at 10:10:11AM -0400, Johannes Weiner wrote: > On Tue, May 26, 2015 at 01:50:06PM +0200, Michal Hocko wrote: > > Please note that this patch introduces a USER VISIBLE CHANGE OF BEHAVIOR. > > Without mm->owner _all_ tasks associated with the mm_struct would > > initiate memcg migration while previously only owner of the mm_struct > > could do that. The original behavior was awkward though because the user > > task didn't have any means to find out the current owner (esp. after > > mm_update_next_owner) so the migration behavior was not well defined > > in general. > > New cgroup API (unified hierarchy) will discontinue tasks file which > > means that migrating threads will no longer be possible. In such a case > > having CLONE_VM without CLONE_THREAD could emulate the thread behavior > > but this patch prevents from isolating memcg controllers from others. > > Nevertheless I am not convinced such a use case would really deserve > > complications on the memcg code side. > > I think such a change is okay. The memcg semantics of moving threads > with the same mm into separate groups have always been arbitrary. No > reasonable behavior can be expected of this, so what sane real life > usecase would rely on it? I suppose that making mm always follow the threadgroup leader should be fine, right? While this wouldn't make any difference in the unified hierarchy, I think this would make more sense for traditional hierarchies. Thanks. -- tejun -- 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>