Messages in this thread | | | Subject | Re: [patch] mm, oom: prevent additional oom kills before memory is freed | From | Tetsuo Handa <> | Date | Thu, 15 Jun 2017 22:01:33 +0900 |
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Michal Hocko wrote: > On Thu 15-06-17 14:03:35, Michal Hocko wrote: > > On Thu 15-06-17 20:32:39, Tetsuo Handa wrote: > > > @@ -556,25 +553,21 @@ static void oom_reap_task(struct task_struct *tsk) > > > struct mm_struct *mm = tsk->signal->oom_mm; > > > > > > /* Retry the down_read_trylock(mmap_sem) a few times */ > > > - while (attempts++ < MAX_OOM_REAP_RETRIES && !__oom_reap_task_mm(tsk, mm)) > > > + while (__oom_reap_task_mm(tsk, mm), !test_bit(MMF_OOM_SKIP, &mm->flags) > > > + && attempts++ < MAX_OOM_REAP_RETRIES) > > > schedule_timeout_idle(HZ/10); > > > > > > - if (attempts <= MAX_OOM_REAP_RETRIES) > > > - goto done; > > > - > > > - > > > - pr_info("oom_reaper: unable to reap pid:%d (%s)\n", > > > - task_pid_nr(tsk), tsk->comm); > > > - debug_show_all_locks(); > > > - > > > -done: > > > - tsk->oom_reaper_list = NULL; > > > - > > > /* > > > * Hide this mm from OOM killer because it has been either reaped or > > > * somebody can't call up_write(mmap_sem). > > > */ > > > - set_bit(MMF_OOM_SKIP, &mm->flags); > > > + if (!test_and_set_bit(MMF_OOM_SKIP, &mm->flags)) { > > > + pr_info("oom_reaper: unable to reap pid:%d (%s)\n", > > > + task_pid_nr(tsk), tsk->comm); > > > + debug_show_all_locks(); > > > + } > > > + > > > > How does this _solve_ anything? Why would you even retry when you > > _know_ that the reference count dropped to zero. It will never > > increment. So the above is basically just schedule_timeout_idle(HZ/10) * > > MAX_OOM_REAP_RETRIES before we set MMF_OOM_SKIP.
If the OOM reaper knows that mm->users == 0, it gives __mmput() some time to "complete exit_mmap() etc. and set MMF_OOM_SKIP". If __mmput() released some memory, subsequent OOM killer invocation is automatically avoided. If __mmput() did not release some memory, let the OOM killer invoke again.
> > Just to make myself more clear. The above assumes that the victim hasn't > passed exit_mmap and MMF_OOM_SKIP in __mmput. Which is the case we want to > address here.
David is trying to avoid setting MMF_OOM_SKIP when the OOM reaper found that mm->users == 0. But we must not wait forever because __mmput() might fail to release some memory immediately. If __mmput() did not release some memory within schedule_timeout_idle(HZ/10) * MAX_OOM_REAP_RETRIES sleep, let the OOM killer invoke again. So, this is the case we want to address here, isn't it?
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