On Wed 26-08-20 20:21:39, xunlei wrote: > On 2020/8/26 下午8:07, Michal Hocko wrote: > > On Wed 26-08-20 20:00:47, xunlei wrote: > >> On 2020/8/26 下午7:00, Michal Hocko wrote: > >>> On Wed 26-08-20 18:41:18, xunlei wrote: > >>>> On 2020/8/26 下午4:11, Michal Hocko wrote: > >>>>> On Wed 26-08-20 15:27:02, Xunlei Pang wrote: > >>>>>> We've met softlockup with "CONFIG_PREEMPT_NONE=y", when > >>>>>> the target memcg doesn't have any reclaimable memory. > >>>>> > >>>>> Do you have any scenario when this happens or is this some sort of a > >>>>> test case? > >>>> > >>>> It can happen on tiny guest scenarios. > >>> > >>> OK, you made me more curious. If this is a tiny guest and this is a hard > >>> limit reclaim path then we should trigger an oom killer which should > >>> kill the offender and that in turn bail out from the try_charge lopp > >>> (see should_force_charge). So how come this repeats enough in your setup > >>> that it causes soft lockups? > >>> > >> > >> should_force_charge() is false, the current trapped in endless loop is > >> not the oom victim. > > > > How is that possible? If the oom killer kills a task and that doesn't > > resolve the oom situation then it would go after another one until all > > tasks are killed. Or is your task living outside of the memcg it tries > > to charge? > > > > All tasks are in memcgs. Looks like the first oom victim is not finished > (unable to schedule), later mem_cgroup_oom()->...->oom_evaluate_task() > will set oc->chosen to -1 and abort. This shouldn't be possible for too long because oom_reaper would make it invisible to the oom killer so it should proceed. Also mem_cgroup_out_of_memory takes a mutex and that is an implicit scheduling point already. Which kernel version is this? And just for the clarification. I am not against the additional cond_resched. That sounds like a good thing in general because we do want to have a predictable scheduling during reclaim which is independent on reclaimability as much as possible. But I would like to drill down to why you are seeing the lockup because those shouldn't really happen. -- Michal Hocko SUSE Labs
