Re: can't oom-kill zap the victim's memory?

[Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>]

Oleg Nesterov wrote:
> > > Hmm. If we already have mmap_sem and started zap_page_range() then
> > > I do not think it makes sense to stop until we free everything we can.
> >
> > Zapping a huge address space can take quite some time
> 
> Yes, and this is another reason we should do this asynchronously.
> 
> > and we really do
> > not have to free it all on behalf of the killer when enough memory is
> > freed to allow for further progress and the rest can be done by the
> > victim. If one batch doesn't seem sufficient then another retry can
> > continue.
> >
> > I do not think that a limited scan would make the implementation more
> > complicated
> 
> But we can't even know much memory unmap_single_vma() actually frees.
> Even if we could, how can we know we freed enough?
> 
> Anyway. Perhaps it makes sense to abort the for_each_vma() loop if
> freed_enough_mem() == T. But it is absolutely not clear to me how we
> should define this freed_enough_mem(), so I think we should do this
> later.

Maybe

  bool freed_enough_mem(void) { !atomic_read(&oom_victims); }

if we change to call mark_oom_victim() on all threads which should be
killed as OOM victims.