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SubjectRe: [PATCH 10/10] mm, oom: hide mm which is shared with kthread or global init
On Wed 15-06-16 16:37:01, Oleg Nesterov wrote:
> Michal,
>
> I am going to ack the whole series, but send some nits/questions,
>
> On 06/09, Michal Hocko wrote:
> >
> > @@ -283,10 +283,22 @@ enum oom_scan_t oom_scan_process_thread(struct oom_control *oc,
> >
> > /*
> > * This task already has access to memory reserves and is being killed.
> > - * Don't allow any other task to have access to the reserves.
> > + * Don't allow any other task to have access to the reserves unless
> > + * the task has MMF_OOM_REAPED because chances that it would release
> > + * any memory is quite low.
> > */
> > - if (!is_sysrq_oom(oc) && atomic_read(&task->signal->oom_victims))
> > - return OOM_SCAN_ABORT;
> > + if (!is_sysrq_oom(oc) && atomic_read(&task->signal->oom_victims)) {
> > + struct task_struct *p = find_lock_task_mm(task);
> > + enum oom_scan_t ret = OOM_SCAN_ABORT;
> > +
> > + if (p) {
> > + if (test_bit(MMF_OOM_REAPED, &p->mm->flags))
> > + ret = OOM_SCAN_CONTINUE;
> > + task_unlock(p);
>
> OK, but perhaps it would be beter to change oom_badness() to return zero if
> MMF_OOM_REAPED is set?

We already do that:
if (adj == OOM_SCORE_ADJ_MIN ||
test_bit(MMF_OOM_REAPED, &p->mm->flags) ||
in_vfork(p)) {
task_unlock(p);
return 0;
}

It is kind of subtle that we have to check it 2 times but we would have
to rework this code much more because oom_badness only can tell to
ignore the task but not to abort scanning altogether currently. If we
should change this I would suggest a separate patch.
--
Michal Hocko
SUSE Labs

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