Hello, On Fri, May 29, 2015 at 04:57:39PM +0200, Michal Hocko wrote: > > > " > > > It also allows several control groups that are virtually grouped by > > > mm_struct, to exist independent of the memory controller i.e., without > > > adding mem_cgroup's for each controller, to mm_struct. > > > " > > > suggests it might have been intentional. That being said, I think it was > > > > I think he's talking about implmenting different controllers which may > > want to add their own css pointer in mm_struct now wouldn't need to as > > the mm is tagged with the owning task from which membership of all > > controllers can be derived. I don't think that's something we need to > > worry about. We haven't seen even a suggestion for such a controller > > and even if that happens we'd be better off adding a separate field > > for the new controller. > > Maybe I've just misunderstood. My understandig was that tasks sharing > the mm could live in different cgroups while the memory would be bound > by a shared memcg. Hmm.... it specifically goes into explaining that it's about having different controllers sharing the owner field. "i.e., without adding mem_cgroup's for each controller, to mm_struct." It seems fairly clear to me. > > I'm a bit lost on what's cleared defined is actually changing. It's > > not like userland had firm control over mm->owner. It was already a > > crapshoot, no? > > OK so you creat a task A (leader) which clones several tasks Pn with > CLONE_VM without CLONE_THREAD. Moving A around would control memcg > membership while Pn could be moved around freely to control membership > in other controllers (e.g. cpu to control shares). So it is something > like moving threads separately. Sure, it'd behave clearly in certain cases but then again you'd have cases where how mm->owner changes isn't clear at all when seen from the userland. e.g. When the original owner goes away, the assignment of the next owner is essentially arbitrary. That's what I meant by saying it was already a crapshoot. We should definitely document the change but this isn't likely to be an issue. CLONE_VM && !CLONE_THREAD is an extreme corner case to begin with and even the behavior there wasn't all that clearly defined. 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>