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From:   Suren Baghdasaryan <surenb@google.com>
Date:   Mon, 23 Oct 2023 12:01:32 -0700
Message-ID: <CAJuCfpF6rfrbT3Sk7+azUH9=CfERYnb84ztoCuA72AxtZ_1FLA@mail.gmail.com>
Subject: Re: [PATCH v3 2/3] userfaultfd: UFFDIO_MOVE uABI
To:     Peter Xu <peterx@redhat.com>
Cc:     akpm@linux-foundation.org, viro@zeniv.linux.org.uk,
        brauner@kernel.org, shuah@kernel.org, aarcange@redhat.com,
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On Mon, Oct 23, 2023 at 11:37=E2=80=AFAM Peter Xu <peterx@redhat.com> 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 pa=
ge
> 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, whic=
h
> 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
>