On Fri, 2 Apr 2010, Oleg Nesterov wrote:
> > > Yes, you are right. OK, oom_badness() can never return points < 0,
> > > we can make it int and oom_badness() can return -1 if !mm. IOW,
> > >
> > > - unsigned int points;
> > > + int points;
> > > ...
> > >
> > > points = oom_badness(...);
> > > if (points >= 0 && (points > *ppoints || !chosen))
> > > chosen = p;
> > >
> >
> > oom_badness() and its predecessor badness() in mainline never return
> > negative scores, so I don't see the value in doing this; just filter the
> > task in select_bad_process() with !p->mm as it has always been done.
>
> David, you continue to ignore my arguments ;) select_bad_process()
> must not filter out the tasks with ->mm == NULL.
>
> Once again:
>
> void *memory_hog_thread(void *arg)
> {
> for (;;)
> malloc(A_LOT);
> }
>
> int main(void)
> {
> pthread_create(memory_hog_thread, ...);
> syscall(__NR_exit, 0);
> }
>
> Now, even if we fix PF_EXITING check, select_bad_process() will always
> ignore this process. The group leader has ->mm == NULL.
>
> See?
>
> That is why I think we need something like find_lock_task_mm() in the
> pseudo-patch I sent.
>
I'm not ignoring your arguments, I think you're ignoring what I'm
responding to. I prefer to keep oom_badness() to be a positive range as
it always has been (and /proc/pid/oom_score has always used an unsigned
qualifier), so I disagree that we need to change oom_badness() to return
anything other than 0 for such tasks. We need to filter them explicitly
in select_bad_process() instead, so please do this there.
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