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

[Suren Baghdasaryan]

On Mon, Oct 23, 2023 at 11:37 AM Peter Xu <peterx@xxxxxxxxxx> wrote:
>
> On Mon, Oct 23, 2023 at 10:43:49AM -0700, Suren Baghdasaryan wrote:
> > > Maybe we should follow what it does with mremap()?  Then your current code
> > > is fine.  Maybe that's the better start.
> >
> > I think that was the original intention, basically treating remapping
> > as a write operation. Maybe I should add a comment here to make it
> > more clear?
>
> Please avoid mention "emulate as a write" - this is not a write, e.g., we
> move a swap entry over without faulting in the page.  We also keep the page
> states, e.g. on hotness.  A write will change all of that.

Understood.

>
> Now rethinking with the recently merged WP_ASYNC: we ignore uffd-wp, which
> means dirty from uffd-wp async tracking POV, that matches with soft-dirty
> always set.  Looks all good.
>
> Perhaps something like "Follow mremap() behavior; ignore uffd-wp for now"
> should work?

Sounds good. Will add in the next version.
Thanks!

>
> --
> Peter Xu
>