Re: [patch 4/7 -mm] oom: badness heuristic rewrite

Minchan Kim
2010-02-17T13:08:27Z

On Wed, 2010-02-17 at 01:23 -0800, David Rientjes wrote:
> On Wed, 17 Feb 2010, Minchan Kim wrote:
>
> > >> Okay. I can think it of slight penalization in this patch.
> > >> But in current OOM logic, we try to kill child instead of forkbomb
> > >> itself. My concern was that.
> > >
> > > We still do with my rewrite, that is handled in oom_kill_process(). The
> > > forkbomb penalization takes place in badness().
> >
> >
> > I thought this patch is closely related to [patch 2/7].
> > I can move this discussion to [patch 2/7] if you want.
> > Another guys already pointed out why we care child.
> >
>
> We have _always_ tried to kill a child of the selected task first if it
> has a seperate address space, patch 2 doesn't change that. It simply
> tries to kill the child with the highest badness() score.

So I mentioned following as.

"Of course, It's not a part of your patch[2/7] which is good.
It has been in there during long time. I hope we could solve that in
this chance."

>
> > I said this scenario is BUGGY forkbomb process. It will fork + exec continuously
> > if it isn't killed. How does user intervene to fix the system?
> > System was almost hang due to unresponsive.
> >
>
> The user would need to kill the parent if it should be killed. The
> unresponsiveness in this example, however, is not a question of the oom
> killer but rather the scheduler to provide interactivity to the user in
> forkbomb scenarios. The oom killer should not create a policy that
> unfairly biases tasks that fork a large number of tasks, however, to
> provide interactivity since that task may be a vital system resource.

As you said, scheduler(or something) can do it with much graceful than
OOM killer. I agreed that.

You wrote "Forkbomb detector" in your patch description. When I saw
that, I thought we need more things to complete forkbomb detection. So I
just suggested my humble idea to fix it in this chance.

>
> > For extreme example,
> > User is writing some important document by OpenOffice and
> > he decided to execute hackbench 1000000 process 1000000.
> >
> > Could user save his important office data without halt if we kill
> > child continuously?
> > I think this scenario can be happened enough if the user didn't know
> > parameter of hackbench.
> >
>
> So what exactly are you proposing we do in the oom killer to distinguish
> between a user's mistake and a vital system resource? I'm personally much
> more concerned with protecting system daemons that provide a service under
> heavyload than protecting against forkbombs in the oom killer.

I don't opposed that. As I said, I just wanted for OOM killer to be more
smart to catch user's mistake. If I understand your opinion,
You said, it's not role of OOM killer but scheduler.

Okay.

--
Kind regards,
Minchan Kim