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. -- Michal Hocko SUSE Labs
