Re: [PATCH 6/9] oom: use same_thread_group instead comparing ->mm

KOSAKI Motohiro
2010-06-17T01:55:52Z

> On 06/16, KOSAKI Motohiro wrote:
> >
> > Now, oom are using "child->mm != p->mm" check to distinguish subthread.
>
> Heh. is it true??? I never undestood what oom_kill_process()->list_for_each_entry()
> is supposed to do.

I guessed. true history was gone long time ago ;)
ok, I'll remove dubious guess.

> > But It's incorrect. vfork() child also have the same ->mm.
>
> Yes.
>
> > This patch change to use same_thread_group() instead.
>
> I don't think we need same_thread_group(). Please note that any children must
> be from the different thread_group.

Agghh. I see.
ok, probably, I've got correct original author intention now.
To be honest, andrea's ancient patch is very hard to understand for me ;)

>
> So,
>
> > --- a/mm/oom_kill.c
> > +++ b/mm/oom_kill.c
> > @@ -161,7 +161,7 @@ unsigned long oom_badness(struct task_struct *p, unsigned long uptime)
> > list_for_each_entry(c, &t->children, sibling) {
> > child = find_lock_task_mm(c);
> > if (child) {
> > - if (child->mm != p->mm)
> > + if (same_thread_group(p, child))
> > points += child->mm->total_vm/2 + 1;
> > task_unlock(child);
> > }
> > @@ -486,7 +486,7 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
> > list_for_each_entry(child, &t->children, sibling) {
> > unsigned long child_points;
> >
> > - if (child->mm == p->mm)
> > + if (same_thread_group(p, child))
> > continue;
>
> In both cases same_thread_group() must be false.
>
> This means that the change in oom_badness() doesn't look right,
> "child->mm != p->mm" is the correct check to decide whether we should
> account child->mm.
>
> The change in oom_kill_process() merely removes this "continue".
> Could someone please explain what this code _should_ do?

I think you are right.