On Tue 19-07-16 19:36:40, Tetsuo Handa wrote: > Michal Hocko wrote: > > On Tue 19-07-16 08:40:48, Michal Hocko wrote: > > > On Tue 19-07-16 06:30:42, Tetsuo Handa wrote: > > > > Michal Hocko wrote: > > > > > I really do not think that this unlikely case really has to be handled > > > > > now. We are very likely going to move to a different model of oom victim > > > > > detection soon. So let's do not add new hacks. exit_oom_victim from > > > > > oom_kill_process just looks like sand in eyes. > > > > > > > > Then, please revert "mm, oom: hide mm which is shared with kthread or global init" > > > > ( http://lkml.kernel.org/r/1466426628-15074-11-git-send-email-mhocko@xxxxxxxxxx ). > > > > I don't like that patch because it is doing pointless find_lock_task_mm() test > > > > and is telling a lie because it does not guarantee that we won't hit OOM livelock. > > > > > > The above patch doesn't make the situation worse wrt livelock. I > > > consider it an improvement. It adds find_lock_task_mm into > > > oom_scan_process_thread but that can hardly be worse than just the > > > task->signal->oom_victims check because we can catch MMF_OOM_REAPED. If > > > we are mm loss, which is a less likely case, then we behave the same as > > > with the previous implementation. > > > > > > So I do not really see a reason to revert that patch for now. > > > > And that being said. If you strongly disagree with the wording then what > > about the following: > > " > > In order to help a forward progress for the OOM killer, make sure that > > this really rare cases will not get into the way and hide the mm from the > > oom killer by setting MMF_OOM_REAPED flag for it. oom_scan_process_thread > > will ignore any TIF_MEMDIE task if it has MMF_OOM_REAPED flag set to catch > > these oom victims. > > > > After this patch we should guarantee a forward progress for the OOM killer > > even when the selected victim is sharing memory with a kernel thread or > > global init as long as the victims mm is still alive. > > " > > No, I don't like "as long as the victims mm is still alive" exception. Why? Because of the wording or in principle? > If you don't like exit_oom_victim() from oom_kill_process(), what about > alternative shown below? > > if (!is_sysrq_oom(oc) && atomic_read(&task->signal->oom_victims)) { > struct task_struct *p = find_lock_task_mm(task); > enum oom_scan_t ret = OOM_SCAN_ABORT; > > if (p) { > if (test_bit(MMF_OOM_REAPED, &p->mm->flags)) > ret = OOM_SCAN_CONTINUE; > task_unlock(p); > +#ifdef CONFIG_MMU > + } else { > + /* > + * MMF_OOM_REAPED was set at oom_kill_process() without > + * waking up the OOM reaper, but this thread group lost > + * its mm. Therefore, pretend as if the OOM reaper lost > + * its mm (i.e. select next OOM victim). > + * But be sure to prevent CONFIG_MMU=n from acting > + * as if exit_oom_victim() in exit_mm() has moved from > + * after mmput() to before mmput(). > + */ > + ret = OOM_SCAN_CONTINUE; > +#endif > } > return ret; > } > > By using this alternative, we can really guarantee a forward progress for > the OOM killer even when the selected victim is sharing memory with a kernel > thread or global init. No "as long as the victims mm is still alive" exception. I wouldn't complicate the pile which is waiting for the merge window and risk introducing some last minute bugs. > Also, this alternative (when combined with removal of MMF_OOM_NOT_REAPABLE) has > a bonus that we no longer need to call exit_oom_victim() from the OOM reaper > because the OOM killer can move on to next OOM victim after the OOM reaper > set MMF_OOM_REAPED to that mm. That is, we can immediately disallow > exit_oom_victim() on remote thread and apply oom_killer_disable() timeout > patch and revert "oom, suspend: fix oom_reaper vs. oom_killer_disable race". > > If we remember victim's mm via your "oom: keep mm of the killed task available" > or my "mm,oom: Use list of mm_struct used by OOM victims.", we can force the > OOM reaper to try to reap by intervening to regular __mmput() from mmput() from > exit_mm() by purposely taking a reference on mm->mm_users. Then, we can always > try to reclaim some memory using the OOM reaper before risking exit_aio() from > __mmput() from mmput() from exit_mm() to stall, for we can keep the OOM killer > waiting until MMF_OOM_REAPED is set using your or my patch. Let's discuss these things later on after merge window along with anothe changes. -- 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>