Michal Hocko wrote: > On Sat 20-02-16 01:01:36, Tetsuo Handa wrote: > > Michal Hocko wrote: > > > On Fri 19-02-16 23:33:31, Tetsuo Handa wrote: > > > > Currently, oom_unkillable_task() is called for twice for each thread, > > > > once at oom_scan_process_thread() and again at oom_badness(). > > > > > > > > The reason oom_scan_process_thread() needs to call oom_unkillable_task() > > > > is to skip TIF_MEMDIE test and oom_task_origin() test if that thread is > > > > not OOM-killable. > > > > > > > > But there is a problem with this ordering, for oom_task_origin() == true > > > > will unconditionally select that thread regardless of oom_score_adj. > > > > When we merge the OOM reaper, the OOM reaper will mark already reaped > > > > process as OOM-unkillable by updating oom_score_adj. In order to avoid > > > > falling into infinite loop, oom_score_adj needs to be checked before > > > > doing oom_task_origin() test. > > > > > > What would be the infinite loop? > > > > Sequence until we merge the OOM reaper: > > > > (1) select_bad_process() returns p due to oom_task_origin(p) == true. > > (2) oom_kill_process() sends SIGKILL to p and sets TIF_MEMDIE on p. > > (3) p gets stuck at down_read(&mm->mmap_sem) in exit_mm(). > > (4) The OOM killer will ignore TIF_MEMDIE on p after some timeout expires. > > (5) select_bad_process() returns p again due to oom_task_origin(p) == true && > > p->mm != NULL. > > And one more thing. The task will stop being oom_task_origin right > after it detects signal pending and retuns from try_to_unuse resp. > unmerge_and_remove_all_rmap_items. That's good. Then, we don't need to worry about oom_task_origin() case. So, the purpose of this "[PATCH] mm,oom: kill duplicated oom_unkillable_task() checks." became only to save oom_unkillable_task() call. I'm trying to update select_bad_process() to use for_each_process() rather than for_each_process_thread(). If we can do it, I think we can use is_oom_victim() and respond to your concern | This will make the scanning much more time consuming (you will check | all the threads in the same thread group for each scanned thread!). I | do not think this is acceptable and it is not really needed for the | !is_sysrq_oom because we are scanning all the threads anyway. while excluding TIF_MEMDIE processes from candidates. -- 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>