On Mon 06-06-22 10:33:30, Michal Hocko wrote: > On Sat 04-06-22 18:35:19, Zackary Liu wrote: > > > > On Jun 1 2022, at 3:45 pm, Michal Hocko <mhocko@xxxxxxxx> wrote: > > > > > On Sat 14-05-22 15:52:28, Zhaoyu Liu wrote: > > >> oom points no longer need to be calculated if a task is oom_task_origin(), > > >> so return 1 to stop the oom_evaluate_task(). > > > > > > This doesn't really explain why this is really desired. Is this a fix, > > > optimization? > > > > > > Please also note that this change has some side effects. For one, the > > > task marked as oom origin will get killed even if there is still a > > > pending oom victim which hasn't been fully dismantled. Is this > > > intentional? > > > > Thank you very much for reminding. > > > > From my point of view, the victim was marked in the last oom, and now it > > has entered the oom again, which means that the system still has no > > deprecated memory available. > > This is not an unusual situation. OOM victims can take some time to die > and release their memory. The oom_reaper is there to fast forward that > process and guarantee a forward progress. But this can still take some > time. Our general policy is to back off when there is an alive oom > victim encountered. Have a look at the tsk_is_oom_victim test in > oom_evaluate_task. For that heuristic to be effective the whole task > list (wether the global one or memcg) has to be evaluated. > > > In order to ensure that the system can > > return to normal as soon as possible, killing the origin task > > immediately should be A good choice, and the role of this patch is to > > end oom_evaluate_task and return true as soon as the origin task is found. > > Could you be more specific how does this patch guarantees a forward > progress? What is the actual usecase that benefits from this change? > > These are all important information for future reference. Please note I > am not saying the patch is wrong. I just still do not see why it is > useful. > > > Maybe this patch is not the optimal solution, it has a trade-off. > > If there are trade-offs, please document them in the changelog. > > The way I see it is that oom_task_origin heuristic has been introduced > to help killing swapoff operation because the swapped out memory doesn't > fit into memory. This is a very reasonable thing to do in general but it > also represents an early failure visible to the userspace. If there is a > pre-existing oom victim then I would argue that we should try to avoid > the failure. Andrew, please drop this patch from your tree. I do not see any real justification here. Thanks! -- Michal Hocko SUSE Labs
