linux-kernel - Re: [PATCH v4 09/10] userfaultfd: update documentation to describe minor fault handling

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Message-ID: <CAJHvVchiABBitTRkr4boSj7pkBN3_y7-1kLVxyhCo5w4m=PEEA@mail.gmail.com>
Date:   Thu, 4 Feb 2021 13:04:16 -0800
From:   Axel Rasmussen <axelrasmussen@...gle.com>
To:     Randy Dunlap <rdunlap@...radead.org>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Chinwen Chang <chinwen.chang@...iatek.com>,
        Huang Ying <ying.huang@...el.com>,
        Ingo Molnar <mingo@...hat.com>, Jann Horn <jannh@...gle.com>,
        Jerome Glisse <jglisse@...hat.com>,
        Lokesh Gidra <lokeshgidra@...gle.com>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Michal Koutný <mkoutny@...e.com>,
        Michel Lespinasse <walken@...gle.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Nicholas Piggin <npiggin@...il.com>,
        Peter Xu <peterx@...hat.com>, Shaohua Li <shli@...com>,
        Shawn Anastasio <shawn@...stas.io>,
        Steven Rostedt <rostedt@...dmis.org>,
        Steven Price <steven.price@....com>,
        Vlastimil Babka <vbabka@...e.cz>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-fsdevel@...r.kernel.org, Linux MM <linux-mm@...ck.org>,
        Adam Ruprecht <ruprecht@...gle.com>,
        Cannon Matthews <cannonmatthews@...gle.com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        David Rientjes <rientjes@...gle.com>,
        Mina Almasry <almasrymina@...gle.com>,
        Oliver Upton <oupton@...gle.com>
Subject: Re: [PATCH v4 09/10] userfaultfd: update documentation to describe
 minor fault handling

On Thu, Feb 4, 2021 at 11:57 AM Randy Dunlap <rdunlap@...radead.org> wrote:
>
> Hi Axel-
>
> one typo found:
>
> On 2/4/21 10:34 AM, Axel Rasmussen wrote:
> > Reword / reorganize things a little bit into "lists", so new features /
> > modes / ioctls can sort of just be appended.
>
> Good plan.
>
> >
> > Signed-off-by: Axel Rasmussen <axelrasmussen@...gle.com>
> > ---
> >  Documentation/admin-guide/mm/userfaultfd.rst | 107 ++++++++++++-------
> >  1 file changed, 66 insertions(+), 41 deletions(-)
> >
> > diff --git a/Documentation/admin-guide/mm/userfaultfd.rst b/Documentation/admin-guide/mm/userfaultfd.rst
> > index 65eefa66c0ba..cfd3daf59d0e 100644
> > --- a/Documentation/admin-guide/mm/userfaultfd.rst
> > +++ b/Documentation/admin-guide/mm/userfaultfd.rst
>
> [snip]
>
> > -
> > -Once the ``userfaultfd`` has been enabled the ``UFFDIO_REGISTER`` ioctl should
> > -be invoked (if present in the returned ``uffdio_api.ioctls`` bitmask) to
> > -register a memory range in the ``userfaultfd`` by setting the
> > +events, except page fault notifications, may be generated:
> > +
> > +- The ``UFFD_FEATURE_EVENT_*`` flags indicate that various other events
> > +  other than page faults are supported. These events are described in more
> > +  detail below in the `Non-cooperative userfaultfd`_ section.
> > +
> > +- ``UFFD_FEATURE_MISSING_HUGETLBFS`` and ``UFFD_FEATURE_MISSING_SHMEM``
> > +  indicate that the kernel supports ``UFFDIO_REGISTER_MODE_MISSING``
> > +  registrations for hugetlbfs and shared memory (covering all shmem APIs,
> > +  i.e. tmpfs, ``IPCSHM``, ``/dev/zero``, ``MAP_SHARED``, ``memfd_create``,
> > +  etc) virtual memory areas, respectively.
> > +
> > +- ``UFFD_FEATURE_MINOR_HUGETLBFS`` indicates that the kernel supports
> > +  ``UFFDIO_REGISTER_MODE_MINOR`` registration for hugetlbfs virtual memory
> > +  areas.
> > +
> > +The userland application should set the feature flags it intends to use
>
> (ah, userspace has moved to userland temporarily. :)

For better or worse, other parts of the document I'm not touching also
use this wording. Maybe we should s/userland/userspace/g, but perhaps
better done as a separate commit to keep this diff focused?
Anecdotally, the use of "userland" doesn't seem to be completely
unprecedented (e.g. grep -r "userland" | wc -l yields 566 matches in
the kernel tree).

I don't have strong feelings, and I was amused by picturing some
Shire-esque countryside with a friendly sign that reads: ~userland
welcomes you~. :)

>
> > +when envoking the ``UFFDIO_API`` ioctl, to request that those features be
>
>         invoking

Whoops! Will send a new version with this fix. Thanks!

>
> > +enabled if supported.
>
>
> thanks.
> --
> ~Randy
>