Michal Hocko wrote: > On Sun 16-07-17 19:59:51, Tetsuo Handa wrote: > > Since the whole memory reclaim path has never been designed to handle the > > scheduling priority inversions, those locations which are assuming that > > execution of some code path shall eventually complete without using > > synchronization mechanisms can get stuck (livelock) due to scheduling > > priority inversions, for CPU time is not guaranteed to be yielded to some > > thread doing such code path. > > > > mutex_trylock() in __alloc_pages_may_oom() (waiting for oom_lock) and > > schedule_timeout_killable(1) in out_of_memory() (already held oom_lock) is > > one of such locations, and it was demonstrated using artificial stressing > > that the system gets stuck effectively forever because SCHED_IDLE priority > > thread is unable to resume execution at schedule_timeout_killable(1) if > > a lot of !SCHED_IDLE priority threads are wasting CPU time [1]. > > I do not understand this. All the contending tasks will go and sleep for > 1s. How can they preempt the lock holder? Not 1s. It sleeps for only 1 jiffies, which is 1ms if CONFIG_HZ=1000. And 1ms may not be long enough to allow the owner of oom_lock when there are many threads doing the same thing. I demonstrated that SCHED_IDLE oom_lock owner is completely defeated by a bunch of !SCHED_IDLE contending threads. -- 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>
