On 4/9/21 2:18 PM, Peter Xu wrote:

On Fri, Apr 09, 2021 at 10:03:53AM -0700, Axel Rasmussen wrote:

quoted

On Thu, Apr 8, 2021 at 10:04 PM Andrew Morton [off-list ref] wrote:

quoted

On Thu,  8 Apr 2021 16:43:18 -0700 Axel Rasmussen [off-list ref] wrote:

quoted

The idea is that it will apply cleanly to akpm's tree, *replacing* the following
patches (i.e., drop these first, and then apply this series):

userfaultfd-support-minor-fault-handling-for-shmem.patch
userfaultfd-support-minor-fault-handling-for-shmem-fix.patch
userfaultfd-support-minor-fault-handling-for-shmem-fix-2.patch
userfaultfd-support-minor-fault-handling-for-shmem-fix-3.patch
userfaultfd-support-minor-fault-handling-for-shmem-fix-4.patch
userfaultfd-selftests-use-memfd_create-for-shmem-test-type.patch
userfaultfd-selftests-create-alias-mappings-in-the-shmem-test.patch
userfaultfd-selftests-reinitialize-test-context-in-each-test.patch
userfaultfd-selftests-exercise-minor-fault-handling-shmem-support.patch

Well.  the problem is,

quoted

+     if (area_alias == MAP_FAILED)
+             err("mmap of memfd alias failed");

`err' doesn't exist until eleventy patches later, in Peter's
"userfaultfd/selftests: unify error handling".  I got tired of (and
lost confidence in) replacing "err(...)" with "fprintf(stderr, ...);
exit(1)" everywhere then fixing up the fallout when Peter's patch came
along.  Shudder.

Oof - sorry about that!

quoted

Sorry, all this material pretty clearly isn't going to make 5.12
(potentially nine days hence), so I shall drop all the userfaultfd
patches.  Let's take a fresh run at all of this after -rc1.

That's okay, my understanding was already that it certainly wouldn't
be in the 5.12 release, but that we might be ready in time for 5.13.

quoted

I have tentatively retained the first series:

userfaultfd-add-minor-fault-registration-mode.patch
userfaultfd-add-minor-fault-registration-mode-fix.patch
userfaultfd-disable-huge-pmd-sharing-for-minor-registered-vmas.patch
userfaultfd-hugetlbfs-only-compile-uffd-helpers-if-config-enabled.patch
userfaultfd-add-uffdio_continue-ioctl.patch
userfaultfd-update-documentation-to-describe-minor-fault-handling.patch
userfaultfd-selftests-add-test-exercising-minor-fault-handling.patch

but I don't believe they have had much testing standalone, without the
other userfaultfd patches present.  So I don't think it's smart to
upstream these in this cycle.  Or I could drop them so you and Peter
can have a clean shot at redoing the whole thing.  Please let me know.

From my perspective, both Peter's error handling and the hugetlbfs
minor faulting patches are ready to go. (Peter's most importantly; we
should establish that as a base, and put all the burden on resolving
conflicts with it on us instead of you :).)

My memory was that Peter's patch was applied before my shmem series,
but it seems I was mistaken. So, maybe the best thing to do is to have
Peter send a version of it based on your tree, without the shmem
series? And then I'll resolve any conflicts in my tree?

It's true that we haven't tested the hugetlbfs minor faults patch
extensively *with the shmem one also applied*, but it has had more
thorough review than the shmem one at this point (e.g. by Mike
Kravetz), and they're rather separate code paths (I'd be surprised if
one breaks the other).

Yes I think the hugetlb part should have got more review done.  IMHO it's a
matter of whether Mike would still like to do a more thorough review, or seems
okay to keep them.

I looked pretty closely at the hugetlb specific parts of the minor fault
handling series.  I only took a high level look at the code modifying and
dealing with the userfaultfd API.  The hugetlb specific parts looked fine
to me.  I can take a closer look at the userfaultfd API modifications,
but it would take more time for me to come up to speed on the APIs.
-- 
Mike Kravetz