On Wed 07-08-13 09:08:36, Tejun Heo wrote: > Hello, Michal. > > On Wed, Aug 07, 2013 at 01:28:26PM +0200, Michal Hocko wrote: > > There is no limit for the maximum number of oom_control events > > registered per memcg. This might lead to an user triggered memory > > depletion if a regular user is allowed to register events. > > > > Let's be more strict and cap the number of events that might be > > registered. MAX_OOM_NOTIFY_EVENTS value is more or less random. The > > expectation is that it should be high enough to cover reasonable > > usecases while not too high to allow excessive resources consumption. > > 1024 events consume something like 24KB which shouldn't be a big deal > > and it should be good enough (even 1024 oom notification events sounds > > crazy). > > I think putting restriction on usage_event makes sense as that builds > a shared contiguous table from all events which can't be attributed > correctly and makes it easy to trigger allocation failures due to > large order allocation but is this necessary for oom and vmpressure, > both of which allocate only for the listening task? Once I was there I made them consistent in that regards. > It isn't different from listening from epoll, for example. epoll limits the number of watchers, no? > If there needs to be kernel memory limit, shouldn't that be handled by > kmemcg? kmemcg would surely help but turning it on just because of potential abuse of the event registration API sounds like an overkill. I think having a cap for user trigable kernel resources is a good thing in general. -- 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>