Re: [PATCH 02/11] x86/mm/hotplug: Remove pgd_list use from the memory hotplug code

Ingo Molnar
2015-09-29T08:42:59Z

* Oleg Nesterov <oleg@redhat.com> wrote:

> On 09/22, Linus Torvalds wrote:
> >
> > However, this now becomes a pattern for the series, and that just makes me think
> >
> > "Why is this not a 'for_each_mm()' pattern helper?"
>
> And we already have other users. And note that oom_kill_process() does _not_
> follow this pattern and that is why it is buggy.
>
> So this is funny, but I was thinking about almost the same, something like
>
> struct task_struct *next_task_with_mm(struct task_struct *p)
> {
> struct task_struct *t;
>
> p = p->group_leader;
> while ((p = next_task(p)) != &init_task) {
> if (p->flags & PF_KTHREAD)
> continue;
>
> t = find_lock_task_mm(p);
> if (t)
> return t;
> }
>
> return NULL;
> }
>
> #define for_each_task_lock_mm(p)
> for (p = &init_task; (p = next_task_with_mm(p)); task_unlock(p))
>
>
> So that you can do
>
> for_each_task_lock_mm(p) {
> do_something_with(p->mm);
>
> if (some_condition()) {
> // UNFORTUNATELY you can't just do "break"
> task_unlock(p);
> break;
> }
> }
>
> do you think it makes sense?

Sure, I'm inclined to use the above code from you.

> In fact it can't be simpler, we can move task_unlock() into next_task_with_mm(),
> it can check ->mm != NULL or p != init_task.

s/can't/can ?

But even with that I'm not sure I can parse your suggestion. Got some (pseudo) code
perhaps?

Thanks,

Ingo