On Tue 23-02-16 14:33:01, David Rientjes wrote: > On Tue, 23 Feb 2016, Michal Hocko wrote: > > > > oom_badness() ranges from 0 (don't kill) to 1000 (please kill). It > > > factors in the setting of /proc/self/oom_score_adj to change that value. > > > That is where OOM_SCORE_ADJ_MIN is enforced. > > > > The question is whether the current placement of OOM_SCORE_ADJ_MIN > > is appropriate. Wouldn't it make more sense to check it in oom_unkillable_task > > instead? > > oom_unkillable_task() deals with the type of task it is (init or kthread) > or being ineligible due to the memcg and cpuset placement. Yes and OOM disabled is yet another condition. > We want to > exclude them from consideration and also suppress them from the task dump > in the kernel log. We don't want to suppress oom disabled processes, we > really want to know their rss, for example. Hmm, is it really helpful though? What would you deduce from seeing a large rss an OOM_SCORE_ADJ_MIN task? Misconfigured system? There must have been a reason to mark the task that way in the first place so you can hardly do anything about it. Moreover you can deduce the same from the available information. I would even argue that displaying OOM_SCORE_ADJ_MIN might be a bit counterproductive because you have to filter them out when looking at the listing. > It could be renamed is_ineligible_task(). That wouldn't really help imho because OOM_SCORE_ADJ_MIN is an uneligible task. > > Sure, checking oom_score_adj under task_lock inside oom_badness will > > prevent from races but the question I raised previously was whether we > > actually care about those races? When would it matter? Is it really > > likely that the update happen during the oom killing? And if yes what > > prevents from the update happening _after_ the check? > > > > It's not necessarily to take task_lock(), but find_lock_task_mm() is the > means we have to iterate threads to find any with memory attached. We > need that logic in oom_badness() to avoid racing with threads that have > entered exit_mm(). It's possible for a thread to have a non-NULL ->mm in > oom_scan_process_thread(), the thread enters exit_mm() without kill, and > oom_badness() can still find it to be eligible because other threads have > not exited. We still want to issue a kill to this process and task_lock() > protects the setting of task->mm to NULL: don't consider it to be a race > in setting oom_score_adj, consider it to be a race in unmapping (but not > freeing) memory in th exit path. I am confused now. This all is true but it is independent on OOM_SCORE_ADJ_MIN check? The check is per signal_struct so checking all the threads will not change anything. -- 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>