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

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  Re: [PATCH 02/11] x86/mm/hotplug: Remove pgd_list use from the memory  hotplug code Linus Torvalds <torvalds@linux-foundation.org> - 2015-09-22 19:50 +0200
    Re: [PATCH 02/11] x86/mm/hotplug: Remove pgd_list use from the  memory hotplug code Oleg Nesterov <oleg@redhat.com> - 2015-09-23 13:50 +0200
      Re: [PATCH 02/11] x86/mm/hotplug: Remove pgd_list use from the  memory hotplug code Ingo Molnar <mingo@kernel.org> - 2015-09-29 10:50 +0200
        Re: [PATCH 02/11] x86/mm/hotplug: Remove pgd_list use from the  memory hotplug code Oleg Nesterov <oleg@redhat.com> - 2015-09-29 19:00 +0200

#1230546 — Re: [PATCH 02/11] x86/mm/hotplug: Remove pgd_list use from the memory hotplug code

On Mon, Sep 21, 2015 at 11:23 PM, Ingo Molnar <mingo@kernel.org> wrote:
> +
> +               for_each_process(g) {
> +                       struct task_struct *p;
> +                       struct mm_struct *mm;
>                         pgd_t *pgd;
>                         spinlock_t *pgt_lock;
>
> +                       p = find_lock_task_mm(g);
> +                       if (!p)
> +                               continue;
> +
> +                       mm = p->mm;

So quite frankly, this is *much* better than the earlier version that
walked over all threads.

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?"

if it only showed up once, that would be one thing. But this
patch-series makes it a thing. Which is why I wonder..

                      Linus
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#1231376 — Re: [PATCH 02/11] x86/mm/hotplug: Remove pgd_list use from the memory hotplug code

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?


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.

Oleg.

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#1234835 — Re: [PATCH 02/11] x86/mm/hotplug: Remove pgd_list use from the memory hotplug code

* 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
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#1235400 — Re: [PATCH 02/11] x86/mm/hotplug: Remove pgd_list use from the memory hotplug code

On 09/29, Ingo Molnar wrote:
>
> * Oleg Nesterov <oleg@redhat.com> wrote:
>
> > 	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 ?

yes, sorry,

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

I meant

	struct task_struct *next_task_lock_mm(struct task_struct *p)
	{
		struct task_struct *t;

		if (p) {
			task_unlock(p);
			p = p->group_leader;
		} else {
			p = &init_task;
		}

		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 = NULL; (p = next_task_lock_mm(p)); )

Oleg.

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