From: "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
To: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: mtk.manpages@gmail.com, Andrea Arcangeli <aarcange@redhat.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
linux-man@vger.kernel.org
Subject: Re: [PATCH man-pages 4/5] userfaultfd.2: add note about asynchronios events delivery
Date: Tue, 2 May 2017 22:27:53 +0200 [thread overview]
Message-ID: <a8acfb52-4e86-b05f-3915-17d2417f81bb@gmail.com> (raw)
In-Reply-To: <20170502094654.GC5910@rapoport-lnx>
On 05/02/2017 11:46 AM, Mike Rapoport wrote:
> On Mon, May 01, 2017 at 08:33:45PM +0200, Michael Kerrisk (man-pages) wrote:
>> Hi Mike,
>>
>> On 05/01/2017 07:43 AM, Mike Rapoport wrote:
>>> Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
>>
>> Thanks. Applied. One question below.
>>
>>> ---
>>> man2/userfaultfd.2 | 12 ++++++++++++
>>> 1 file changed, 12 insertions(+)
>>>
>>> diff --git a/man2/userfaultfd.2 b/man2/userfaultfd.2
>>> index 8b89162..f177bba 100644
>>> --- a/man2/userfaultfd.2
>>> +++ b/man2/userfaultfd.2
>>> @@ -112,6 +112,18 @@ created for the child process,
>>> which allows userfaultfd monitor to perform user-space paging
>>> for the child process.
>>>
>>> +Unlike page faults which have to be synchronous and require
>>> +explicit or implicit wakeup,
>>> +all other events are delivered asynchronously and
>>> +the non-cooperative process resumes execution as
>>> +soon as manager executes
>>> +.BR read(2).
>>> +The userfaultfd manager should carefully synchronize calls
>>> +to UFFDIO_COPY with the events processing.
>>> +
>>> +The current asynchronous model of the event delivery is optimal for
>>> +single threaded non-cooperative userfaultfd manager implementations.
>>
>> The preceding paragraph feels incomplete. It seems like you want to make
>> a point with that last sentence, but the point is not explicit. What's
>> missing?
>
> I've copied both from Documentation/vm/userfaulftfd.txt, and there we also
> talk about possibility of addition of synchronous events delivery and
> that makes the paragraph above to seem crippled :)
> The major point here is that current events delivery model could be
> problematic for multi-threaded monitor. I even suspect that it would be
> impossible to ensure synchronization between page faults and non-page
> fault events in multi-threaded monitor.
Okay -- thanks for the info. I've noted it, but won't make changes
any changes to the page for now.
Cheers,
Michael
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
next prev parent reply other threads:[~2017-05-02 20:28 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-01 5:43 [PATCH man-pages 0/5] {ioctl_}userfaultfd.2: yet another update Mike Rapoport
2017-05-01 5:43 ` [PATCH man-pages 1/5] ioctl_userfaultfd.2: update description of shared memory areas Mike Rapoport
2017-05-01 18:33 ` Michael Kerrisk (man-pages)
2017-05-02 9:31 ` Mike Rapoport
2017-05-02 20:23 ` Michael Kerrisk (man-pages)
2017-05-01 5:43 ` [PATCH man-pages 2/5] ioctl_userfaultfd.2: UFFDIO_COPY: add ENOENT and ENOSPC description Mike Rapoport
2017-05-01 18:33 ` Michael Kerrisk (man-pages)
2017-05-01 5:43 ` [PATCH man-pages 3/5] ioctl_userfaultfd.2: add BUGS section Mike Rapoport
2017-05-01 18:33 ` Michael Kerrisk (man-pages)
2017-05-02 9:32 ` Mike Rapoport
2017-05-01 5:43 ` [PATCH man-pages 4/5] userfaultfd.2: add note about asynchronios events delivery Mike Rapoport
2017-05-01 18:33 ` Michael Kerrisk (man-pages)
2017-05-02 9:46 ` Mike Rapoport
2017-05-02 20:27 ` Michael Kerrisk (man-pages) [this message]
2017-05-01 5:43 ` [PATCH man-pages 5/5] userfaultfd.2: update VERSIONS section with 4.11 chanegs Mike Rapoport
2017-05-01 18:33 ` Michael Kerrisk (man-pages)
2017-05-01 18:34 ` [PATCH man-pages 0/5] {ioctl_}userfaultfd.2: yet another update Michael Kerrisk (man-pages)
2017-05-02 9:48 ` Mike Rapoport
2017-05-02 20:28 ` Michael Kerrisk (man-pages)
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