On Thu 07-04-16 20:55:34, Tetsuo Handa wrote: > Michal Hocko wrote: > > The first obvious one is when the oom victim clears its mm and gets > > stuck later on. oom_reaper would back of on find_lock_task_mm returning > > NULL. We can safely try to clear TIF_MEMDIE in this case because such a > > task would be ignored by the oom killer anyway. The flag would be > > cleared by that time already most of the time anyway. > > I didn't understand what this wants to tell. The OOM victim will clear > TIF_MEMDIE as soon as it sets current->mm = NULL. No it clears the flag _after_ it returns from mmput. There is no guarantee it won't get stuck somewhere on the way there - e.g. exit_aio waits for completion and who knows what else might get stuck. > Even if the oom victim > clears its mm and gets stuck later on (e.g. at exit_task_work()), > TIF_MEMDIE was already cleared by that moment by the OOM victim. > > > > > The less obvious one is when the oom reaper fails due to mmap_sem > > contention. Even if we clear TIF_MEMDIE for this task then it is not > > very likely that we would select another task too easily because > > we haven't reaped the last victim and so it would be still the #1 > > candidate. There is a rare race condition possible when the current > > victim terminates before the next select_bad_process but considering > > that oom_reap_task had retried several times before giving up then > > this sounds like a borderline thing. > > Is it helpful? Allowing the OOM killer to select the same thread again > simply makes the kernel log buffer flooded with the OOM kill messages. I am trying to be as conservative as possible here. The likelyhood of mmap sem contention will be reduced considerably after my down_write_killable series will get merged. If this turns out to be a problem (trivial to spot as the same task will be killed again) then we can think about a fix for that (e.g. ignore the task if the has been selected more than N times). > I think we should not allow the OOM killer to select the same thread again > by e.g. doing tsk->signal->oom_score_adj = OOM_SCORE_ADJ_MIN regardless of > whether reaping that thread's memory succeeded or not. I think this comes with some risk and so it should go as a separate patch with a full justification why the outcome is better. Especially after the mmap_sem contention will be reduced by other means. -- 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>