Re: [PATCH v4 1/2] mm: introduce process_mrelease system call

[Suren Baghdasaryan]

On Tue, Aug 3, 2021 at 11:21 PM Michal Hocko <mhocko@xxxxxxxx> wrote:
>
> On Tue 03-08-21 15:09:43, Suren Baghdasaryan wrote:
> > On Tue, Aug 3, 2021 at 10:27 AM Suren Baghdasaryan <surenb@xxxxxxxxxx> wrote:
> [...]
> > > > > +     if (task_will_free_mem(task) && (task->flags & PF_KTHREAD) == 0) {
> > > > > +             mm = task->mm;
> > > > > +             mmget(mm);
> > > > > +     }
> > > > > +     task_unlock(task);
> > > > > +     if (!mm) {
> > > >
> > > > Do we want to treat MMF_OOM_SKIP as a failure?
> > >
> > > Yeah, I don't think we want to create additional contention if
> > > oom-killer is already working on this mm. Should we return EBUSY in
> > > this case? Other possible options is ESRCH, indicating that this
> > > process is a goner, so don't bother. WDYT?
> >
> > After considering this some more I think ESRCH would be more
> > appropriate. EBUSY might be understood as "I need to retry at a better
> > time", which is not what we want here.
>
> Why cannot we simply return 0 in that case. The work has been done
> already by the kernel so why should we tell the caller that there was
> something wrong?

Ah, you are right. I was under the impression that MMF_OOM_SKIP means
oom-killer is reaping the mm, but looks like it means that mm was
already reaped. If that's true then I agree, returning 0 is the right
move here. Will fix.

>
> --
> Michal Hocko
> SUSE Labs