Hi Shakeel, On Thu, Jan 10, 2019 at 09:44:32AM -0800, Shakeel Butt wrote: > If a memcg is over high limit, memory reclaim is scheduled to run on > return-to-userland. However it is assumed that the memcg is the current > process's memcg. With remote memcg charging for kmem or swapping in a > page charged to remote memcg, current process can trigger reclaim on > remote memcg. So, schduling reclaim on return-to-userland for remote > memcgs will ignore the high reclaim altogether. So, record the memcg > needing high reclaim and trigger high reclaim for that memcg on > return-to-userland. However if the memcg is already recorded for high > reclaim and the recorded memcg is not the descendant of the the memcg > needing high reclaim, punt the high reclaim to the work queue.
The idea behind remote charging is that the thread allocating the memory is not responsible for that memory, but a different cgroup is. Why would the same thread then have to work off any high excess this could produce in that unrelated group? Say you have a inotify/dnotify listener that is restricted in its memory use - now everybody sending notification events from outside that listener's group would get throttled on a cgroup over which it has no control. That sounds like a recipe for priority inversions. It seems to me we should only do reclaim-on-return when current is in the ill-behaved cgroup, and punt everything else - interrupts and remote charges - to the workqueue.
