Re: [PATCH v4 03/10] userfaultfd/shmem: support UFFDIO_CONTINUE for shmem

Peter Xu
2021-04-27T18:03:26Z

On Tue, Apr 27, 2021 at 09:57:16AM -0700, Axel Rasmussen wrote:
> I'd prefer to keep them separate, as they are not tiny patches (they
> are roughly +200/-150 each). And, they really are quite independent -
> at least in the sense that I can reorder them via rebase with no
> conflicts, and the code builds at each commit in either orientation. I
> think this implies they're easier to review separately, rather than
> squashed.
>
> I don't have a strong feeling about the order. I slightly prefer
> swapping them compared to this v4 series: first introduce minor
> faults, then introduce CONTINUE.
>
> Since Peter also has no strong opinion, and Hugh it sounds like you
> prefer it the other way around, I'll swap them as we had in some
> previous version of this series: first introduce minor faults, then
> introduce CONTINUE.

Yes I have no strong opinion, but that's probably the least I prefer. :-)

Because you'll declare UFFD_FEATURE_MINOR_SHMEM and enable this feature without
the feature being completely implemented (without UFFDIO_CONTINUE, it's not
complete since no one will be able to resolve that minor fault).

Not a big deal anyway, but since we're at it... Basically I think three things
to do for minor shmem support:

(1) UFFDIO_CONTINUE (resolving path)
(2) Handle fault path for shmem minor fault (faulting path)
(3) Enablement of UFFD_FEATURE_MINOR_SHMEM (from which point, user can detect
and enable it)

I have no preference on how you'd like to merge these steps (right now you did
1 first, then 2+3 later; or as Hugh suggested do 1+2+3 together), but I'd still
hope item 3 should always be the last, if possible...

Thanks,

--
Peter Xu