On Thu, Nov 06, 2014 at 05:02:23PM +0100, Michal Hocko wrote: > > Why would PM freezing make OOM killing fail? That doesn't make much > > sense. Sure, it can block it for a finite duration for sync purposes > > but making OOM killing fail seems the wrong way around. > > We cannot block in the allocation path because the request might come > from the freezer path itself (e.g. when suspending devices etc.). > At least this is my understanding why the original oom disable approach > was implemented. I was saying that it could temporarily block either direction to implement proper synchronization while guaranteeing forward progress. > > We're doing one thing for non-PM freezing and the other way around for > > PM freezing, which indicates one of the two directions is wrong. > > Because those two paths are quite different in their requirements. The > cgroup freezer only cares about freezing tasks and it doesn't have to > care about tasks accessing a possibly half suspended device on their way > out. I don't think the fundamental relationship between freezing and oom killing are different between the two and the failure to recognize that is what's leading to these weird issues. > > Shouldn't it be that OOM killing happening while PM freezing is in > > progress cancels PM freezing rather than the other way around? Find a > > point in PM suspend/hibernation operation where everything must be > > stable, disable OOM killing there and check whether OOM killing > > happened inbetween and if so back out. > > This is freeze_processes AFAIU. I might be wrong of course but this is > the time since when nobody should be waking processes up because they > could access half suspended devices. No, you're doing it before freezing starts. The system is in no way in a quiescent state at that point. > > It seems rather obvious to me that OOM killing has to have precedence > > over PM freezing. > > > > Sure, once the system reaches a point where the whole system must be > > in a stable state for snapshotting or whatever, disabling OOM killing > > is fine but at that point the system is in a very limited execution > > mode and sure won't be processing page faults from userland for > > example and we can actually disable OOM killing knowing that anything > > afterwards is ready to handle memory allocation failures. > > I am really confused now. This is basically what the final patch does > actually. Here is the what I have currently just to make the further > discussion easier. Please see above. -- 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>