Re: [PATCH v3 2/3] userfaultfd: UFFDIO_MOVE uABI

[David Hildenbrand]

On 23.10.23 14:03, David Hildenbrand wrote:
> On 22.10.23 17:46, Peter Xu wrote:
> > On Fri, Oct 20, 2023 at 07:16:19PM +0200, David Hildenbrand wrote:
> > > These are rather the vibes I'm getting from Peter. "Why rename it, could
> > > confuse people because the original patches are old", "Why exclude it if it
> > > has been included in the original patches". Not the kind of reasoning I can
> > > relate to when it comes to upstreaming some patches.
> >
> > You can't blame anyone if you misunderstood and biased the question.
> >
> > The first question is definitely valid, even until now.  You guys still
> > prefer to rename it, which I'm totally fine with.
> >
> > The 2nd question is wrong from your interpretation.  That's not my point,
> > at least not starting from a few replies already.  What I was asking for is
> > why such page movement between mm is dangerous.  I don't think I get solid
> > answers even until now.
> >
> > Noticing "memcg is missing" is not an argument for "cross-mm is dangerous",
> > it's a review comment.  Suren can address that.
> >
> > You'll propose a new feature that may tag an mm is not an argument either,
> > if it's not merged yet.  We can also address that depending on what it is,
> > also on which lands earlier.
> >
> > It'll be good to discuss these details even in a single-mm support.  Anyone
> > would like to add that can already refer to discussion in this thread.
> >
> > I hope I'm clear.
>
> I said everything I had to say, go read what I wrote.

Re-read your message after flying over first couple of paragraphs 
previously a bit quick too quickly (can easily happen when I'm told that 
I misunderstand questions and read them in a "biased" way).

I'll happy to discuss cross-mm support once we actually need it. I just 
don't see the need to spend any energy on that right now, without any 
users on the horizon.

[(a) I didn't blame anybody, I said that I don't understand the 
reasoning. (b) I hope I made it clear that this is added complexity (and 
not just currently dangerous) and so far I haven't heard a compelling 
argument why we should do any of that or even spend our time discussing 
that. (c) I never used "memcg is missing" as an argument for "cross-mm 
is dangerous", all about added complexity without actual users. (d) "it 
easily shows that there are cases  where this will require extra work -- 
without any current benefits" -- is IMHO a perfectly fine argument 
against complexity that currently nobody needs]

--
Cheers,

David / dhildenb