On Mon, 2017-07-31 at 16:38 -0400, Johannes Weiner wrote: > On Mon, Jul 31, 2017 at 09:49:39PM +0200, Mike Galbraith wrote: > > On Mon, 2017-07-31 at 14:41 -0400, Johannes Weiner wrote: > > > > > > Adding an rq counter for tasks inside memdelay sections should be > > > straight-forward as well (except for maybe the migration cost of that > > > state between CPUs in ttwu that Mike pointed out). > > > > What I pointed out should be easily eliminated (zero use case). > > How so? I was thinking along the lines of schedstat_enabled(). > > > That leaves the question of how to track these numbers per cgroup at > > > an acceptable cost. The idea for a tree of cgroups is that walltime > > > impact of delays at each level is reported for all tasks at or below > > > that level. E.g. a leave group aggregates the state of its own tasks, > > > the root/system aggregates the state of all tasks in the system; hence > > > the propagation of the task state counters up the hierarchy. > > > > The crux of the biscuit is where exactly the investment return lies. > > Gathering of these numbers ain't gonna be free, no matter how hard you > > try, and you're plugging into paths where every cycle added is made of > > userspace hide. > > Right. But how to implement it sanely and optimize for cycles, and > whether we want to default-enable this interface are two separate > conversations. > > It makes sense to me to first make the implementation as lightweight > on cycles and maintainability as possible, and then worry about the > cost / benefit defaults of the shipped Linux kernel afterwards. > > That goes for the purely informative userspace interface, anyway. The > easily-provoked thrashing livelock I have described in the email to > Andrew is a different matter. If the OOM killer requires hooking up to > this metric to fix it, it won't be optional. But the OOM code isn't > part of this series yet, so again a conversation best had later, IMO. If that "the many must pay a toll to save the few" conversation ever happens, just recall me registering my boo/hiss in advance. I don't have to feel guilty about not liking the idea of making donations to feed the poor starving proggies ;-) -Mike -- 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
