On Tue 23-10-18 21:33:43, Tetsuo Handa wrote: > On 2018/10/23 21:10, Michal Hocko wrote: > > On Tue 23-10-18 13:42:46, Michal Hocko wrote: > >> On Tue 23-10-18 10:01:08, Tetsuo Handa wrote: > >>> Michal Hocko wrote: > >>>> On Mon 22-10-18 20:45:17, Tetsuo Handa wrote: > >>>>>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c > >>>>>> index e79cb59552d9..a9dfed29967b 100644 > >>>>>> --- a/mm/memcontrol.c > >>>>>> +++ b/mm/memcontrol.c > >>>>>> @@ -1380,10 +1380,22 @@ static bool mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask, > >>>>>> .gfp_mask = gfp_mask, > >>>>>> .order = order, > >>>>>> }; > >>>>>> - bool ret; > >>>>>> + bool ret = true; > >>>>>> > >>>>>> mutex_lock(&oom_lock); > >>>>>> + > >>>>>> + /* > >>>>>> + * multi-threaded tasks might race with oom_reaper and gain > >>>>>> + * MMF_OOM_SKIP before reaching out_of_memory which can lead > >>>>>> + * to out_of_memory failure if the task is the last one in > >>>>>> + * memcg which would be a false possitive failure reported > >>>>>> + */ > >>>>>> + if (tsk_is_oom_victim(current)) > >>>>>> + goto unlock; > >>>>>> + > >>>>> > >>>>> This is not wrong but is strange. We can use mutex_lock_killable(&oom_lock) > >>>>> so that any killed threads no longer wait for oom_lock. > >>>> > >>>> tsk_is_oom_victim is stronger because it doesn't depend on > >>>> fatal_signal_pending which might be cleared throughout the exit process. > >>>> > >>> > >>> I still want to propose this. No need to be memcg OOM specific. > >> > >> Well, I maintain what I've said [1] about simplicity and specific fix > >> for a specific issue. Especially in the tricky code like this where all > >> the consequences are far more subtle than they seem to be. > >> > >> This is obviously a matter of taste but I don't see much point discussing > >> this back and forth for ever. Unless there is a general agreement that > >> the above is less appropriate then I am willing to consider a different > >> change but I simply do not have energy to nit pick for ever. > >> > >> [1] http://lkml.kernel.org/r/20181022134315.GF18839@xxxxxxxxxxxxxx > > > > In other words. Having a memcg specific fix means, well, a memcg > > maintenance burden. Like any other memcg specific oom decisions we > > already have. So are you OK with that Johannes or you would like to see > > a more generic fix which might turn out to be more complex? > > > > I don't know what "that Johannes" refers to. let me rephrase Johannes, are you OK with that (memcg specific fix) or you would like to see a more generic fix which might turn out to be more complex. -- Michal Hocko SUSE Labs
