Re: [PATCH] mm,oom: Try last second allocation before and after selecting an OOM victim.

[Tetsuo Handa]

Michal Hocko wrote:
> On Tue 31-10-17 21:42:23, Tetsuo Handa wrote:
> > > While both have some merit, the first reason is mostly historical
> > > because we have the explicit locking now and it is really unlikely that
> > > the memory would be available right after we have given up trying.
> > > Last attempt allocation makes some sense of course but considering that
> > > the oom victim selection is quite an expensive operation which can take
> > > a considerable amount of time it makes much more sense to retry the
> > > allocation after the most expensive part rather than before. Therefore
> > > move the last attempt right before we are trying to kill an oom victim
> > > to rule potential races when somebody could have freed a lot of memory
> > > in the meantime. This will reduce the time window for potentially
> > > pre-mature OOM killing considerably.
> > 
> > But this is about "doing last second allocation attempt after selecting
> > an OOM victim". This is not about "allowing OOM victims to try ALLOC_OOM
> > before selecting next OOM victim" which is the actual problem I'm trying
> > to deal with.
> 
> then split it into two. First make the general case and then add a more
> sophisticated on top. Dealing with multiple issues at once is what makes
> all those brain cells suffer.

I'm failing to understand. I was dealing with single issue at once.
The single issue is "MMF_OOM_SKIP prematurely prevents OOM victims from trying
ALLOC_OOM before selecting next OOM victims". Then, what are the general case and
a more sophisticated? I wonder what other than "MMF_OOM_SKIP should allow OOM
victims to try ALLOC_OOM for once before selecting next OOM victims" can exist...