On Mon 01-07-19 22:38:58, Tetsuo Handa wrote: > On 2019/07/01 22:17, Michal Hocko wrote: > > On Mon 01-07-19 22:04:22, Tetsuo Handa wrote: > >> But I realized that this patch was too optimistic. We need to wait for mm-less > >> threads until MMF_OOM_SKIP is set if the process was already an OOM victim. > > > > If the process is an oom victim then _all_ threads are so as well > > because that is the address space property. And we already do check that > > before reaching oom_badness IIRC. So what is the actual problem you are > > trying to solve here? > > I'm talking about behavioral change after tsk became an OOM victim. > > If tsk->signal->oom_mm != NULL, we have to wait for MMF_OOM_SKIP even if > tsk->mm == NULL. Otherwise, the OOM killer selects next OOM victim as soon as > oom_unkillable_task() returned true because has_intersects_mems_allowed() returned > false because mempolicy_nodemask_intersects() returned false because all thread's > mm became NULL (despite tsk->signal->oom_mm != NULL). OK, I finally got your point. It was not clear that you are referring to the code _after_ the patch you are proposing. You are indeed right that this would have a side effect that an additional victim could be selected even though the current process hasn't terminated yet. Sigh, another example how the whole thing is subtle so I retract my Ack and request a real life example of where this matters before we think about a proper fix and make the code even more complex. -- Michal Hocko SUSE Labs
