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    SubjectRe: [PATCH v2 2/3] userfaultfd: UFFDIO_REMAP uABI
    On 04.10.23 01:39, Lokesh Gidra wrote:
    > On Tue, Oct 3, 2023 at 11:26 PM Suren Baghdasaryan <surenb@google.com> wrote:
    >>
    >> On Tue, Oct 3, 2023 at 2:21 PM Peter Xu <peterx@redhat.com> wrote:
    >>>
    >>> On Tue, Oct 03, 2023 at 11:08:07PM +0200, David Hildenbrand wrote:
    >>>> Sorry I have to ask: has this ever been discussed on the list? I don't see
    >>>> any pointers. If not, then probably the number of people that know about the
    >>>> history can be counted with my two hands and that shouldn't be the basis for
    >>>> making decisions.
    >>>
    >>> For example:
    >>>
    >>> https://lore.kernel.org/all/1425575884-2574-21-git-send-email-aarcange@redhat.com/

    Sorry, I had to process a family NMI the last couple of days.

    >>
    >> There was another submission in 2019:
    >> https://lore.kernel.org/all/cover.1547251023.git.blake.caldwell@colorado.edu/

    It would be good to link them in the cover letter and shortly explain
    why that wasn't merged back then (if there was any reason).

    >>
    >> Though both times it did not generate much discussion. I don't have a
    >> strong preference though MOVE sounds more generic to me TBH (it
    >> specifies the operation rather than REMAP which hints on how that
    >> operation is carried out). But again, I'm fine either way.
    >
    > That's a good point. IMHO, if in future we want to have the fallback
    > implemented, then MOVE would be a more appropriate name than REMAP.
    >
    >> As for UFFDIO_MOVE_ZERO_COPY_ONLY vs UFFDIO_MOVE_MODE_ALLOW_COPY, I
    >> find it weird that the default (the most efficient/desired) mode of
    >> operation needs a flag. I would prefer to have no flag initially and
    >> add UFFDIO_MOVE_MODE_ALLOW_COPY or whatever name is more appropriate
    >> when/if we ever need it. Makes sense?
    >
    > Agreed!

    I agree. One could have UFFDIO_MOVE that is best-effort and documented
    like that, and a to-be-named future extension that always works but
    might be more expensive.


    Ideally we'd have an interface that does not expose and/or rely on such
    low-level information and simply always works, but getting that would
    mean that we'd have to implement the fallback immediately ... so I guess
    we'll have to expose a best-effort interface first.

    --
    Cheers,

    David / dhildenb

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