Re: [PATCH 4/3] mm, oom: drop the last allocation attempt before out_of_memory

[Tetsuo Handa]

Michal Hocko wrote:
> > https://lkml.org/lkml/2015/3/25/40
> > 
> > We could have out_of_memory() wait until the number of outstanding OOM
> > victims drops to 0. Then __alloc_pages_may_oom() doesn't relinquish
> > the lock until its kill has been finalized:
> > 
> > diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> > index 914451a..4dc5b9d 100644
> > --- a/mm/oom_kill.c
> > +++ b/mm/oom_kill.c
> > @@ -892,7 +892,9 @@ bool out_of_memory(struct oom_control *oc)
> >  		 * Give the killed process a good chance to exit before trying
> >  		 * to allocate memory again.
> >  		 */
> > -		schedule_timeout_killable(1);
> > +		if (!test_thread_flag(TIF_MEMDIE))
> > +			wait_event_timeout(oom_victims_wait,
> > +					   !atomic_read(&oom_victims), HZ);
> >  	}
> >  	return true;
> >  }
> 
> Yes this makes sense to me

I think schedule_timeout_killable(1) was used for handling cases
where current thread did not get TIF_MEMDIE but got SIGKILL due to
sharing the victim's memory. If current thread is blocking TIF_MEMDIE
thread, this can become a needless delay.

Also, I don't know whether using wait_event_*() helps handling a
problem that schedule_timeout_killable(1) can sleep for many minutes
with oom_lock held when there are a lot of tasks. Detail is explained
in my proposed patch.