On Tue 08-01-19 05:59:49, Tetsuo Handa wrote: > On 2019/01/07 23:38, Michal Hocko wrote: > > From: Michal Hocko <mhocko@xxxxxxxx> > > > > Tetsuo has reported [1] that a single process group memcg might easily > > swamp the log with no-eligible oom victim reports due to race between > > the memcg charge and oom_reaper > > This explanation is outdated. I reported that one memcg OOM killer can > kill all processes in that memcg. I expect the changelog to be updated. I am open to refinements. Any specific wording you have in mind? > > > > Thread 1 Thread2 oom_reaper > > try_charge try_charge > > mem_cgroup_out_of_memory > > mutex_lock(oom_lock) > > mem_cgroup_out_of_memory > > mutex_lock(oom_lock) > > out_of_memory > > select_bad_process > > oom_kill_process(current) > > wake_oom_reaper > > oom_reap_task > > MMF_OOM_SKIP->victim > > mutex_unlock(oom_lock) > > out_of_memory > > select_bad_process # no task > > > > If Thread1 didn't race it would bail out from try_charge and force the > > charge. We can achieve the same by checking tsk_is_oom_victim inside > > the oom_lock and therefore close the race. > > > > [1] http://lkml.kernel.org/r/bb2074c0-34fe-8c2c-1c7d-db71338f1e7f@xxxxxxxxxxxxxxxxxxx > > Signed-off-by: Michal Hocko <mhocko@xxxxxxxx> > > --- > > mm/memcontrol.c | 14 +++++++++++++- > > 1 file changed, 13 insertions(+), 1 deletion(-) > > > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > > index af7f18b32389..90eb2e2093e7 100644 > > --- a/mm/memcontrol.c > > +++ b/mm/memcontrol.c > > @@ -1387,10 +1387,22 @@ 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); > > And because of "[PATCH 1/2] mm, oom: marks all killed tasks as oom > victims", mark_oom_victim() will be called on current thread even if > we used mutex_lock_killable(&oom_lock) here, like you said > > mutex_lock_killable would take care of exiting task already. I would > then still prefer to check for mark_oom_victim because that is not racy > with the exit path clearing signals. I can update my patch to use > _killable lock variant if we are really going with the memcg specific > fix. > > . If current thread is not yet killed by the OOM killer but can terminate > without invoking the OOM killer, using mutex_lock_killable(&oom_lock) here > saves some processes. What is the race you are referring by "racy with the > exit path clearing signals" ? This is unrelated to the patch. > > + > > + /* > > + * 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 > > + */ > > Not only out_of_memory() failure. Current thread needlessly tries to > select next OOM victim. out_of_memory() failure is nothing but a result > of no eligible candidate case. So? Let me ask again. Does this solve the issue you are seeing? I really do not want to end in nit picking endless thread again and would like to move on. > > + if (tsk_is_oom_victim(current)) > > + goto unlock; > > + > > ret = out_of_memory(&oc); > > + > > +unlock: > > mutex_unlock(&oom_lock); > > return ret; > > } > > -- Michal Hocko SUSE Labs
