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SubjectRe: [patch] oom: give current access to memory reserves if it has been killed
On 04/01, David Rientjes wrote:
>
> On Wed, 31 Mar 2010, Oleg Nesterov wrote:
>
> > Probably something like the patch below makes sense. Note that
> > "skip kernel threads" logic is wrong too, we should check PF_KTHREAD.
> > Probably it is better to check it in select_bad_process() instead,
> > near is_global_init().
>
> is_global_init() will be true for p->flags & PF_KTHREAD.

No, is_global_init() && PF_KTHREAD have nothing to do with each other.

> > @@ -159,13 +172,9 @@ unsigned int oom_badness(struct task_str
> > if (p->flags & PF_OOM_ORIGIN)
> > return 1000;
> >
> > - task_lock(p);
> > - mm = p->mm;
> > - if (!mm) {
> > - task_unlock(p);
> > + p = find_lock_task_mm(p);
> > + if (!p)
> > return 0;
> > - }
> > -
> > /*
> > * The baseline for the badness score is the proportion of RAM that each
> > * task's rss and swap space use.
> > @@ -330,12 +339,6 @@ static struct task_struct *select_bad_pr
> > *ppoints = 1000;
> > }
> >
> > - /*
> > - * skip kernel threads and tasks which have already released
> > - * their mm.
> > - */
> > - if (!p->mm)
> > - continue;
> > if (p->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
> > continue;
>
> You can't do this for the reason I cited in another email, oom_badness()
> returning 0 does not exclude a task from being chosen by
> selcet_bad_process(), it will use that task if nothing else has been found
> yet. We must explicitly filter it from consideration by checking for
> !p->mm.

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;
Oleg.



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