Re: [RFC 00/11] DAX fsynx/msync support

From	Jeff Moyer <jmoyer@redhat.com>
Newsgroups	linux.kernel
Subject	Re: [RFC 00/11] DAX fsynx/msync support
Date	2015-11-05 20:50 +0100
Message-ID	<qryHL-2vb-1@gated-at.bofh.it> (permalink)
References	(3 earlier) <qqao9-6f8-1@gated-at.bofh.it> <qqohr-6oB-21@gated-at.bofh.it> <qqtK9-1nc-1@gated-at.bofh.it> <qquwy-1Uo-7@gated-at.bofh.it> <qrofo-4bJ-9@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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Dave Chinner <david@fromorbit.com> writes:

>> But this part is not.  It is up to the I/O scheduler to decide when to
>> dispatch requests.  It can hold on to them for a variety of reasons.
>> Flush requests, however, do not go through the I/O scheduler.  At the
>
> That's pure REQ_FLUSH bios, right? Aren't data IOs with
> REQ_FLUSH|REQ_FUA sorted like any other IO?

No, they also go through the flush machinery, and so short-circuit the
I/O scheduler.

>> Des xfs rely on this model for correctness?  If so, I'd say we've got a
>> problem
>
> No, it doesn't. The XFS integrity model doesn't trust the IO layers
> to tell the truth about IO ordering and completion or for it's
> developers to fully understand how IO layer ordering works. :P
>
> i.e. we wait for full completions of all dependent IO before issuing
> flushes or log writes that use REQ_FLUSH|REQ_FUA semantics to ensure
> the dependent IOs are fully caught by the cache flushes...

OK, phew!  ;-)

-Jeff
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Thread

Re: [RFC 00/11] DAX fsynx/msync support Dave Chinner <david@fromorbit.com> - 2015-11-02 00:40 +0100
  Re: [RFC 00/11] DAX fsynx/msync support Jeff Moyer <jmoyer@redhat.com> - 2015-11-02 15:30 +0100
    Re: [RFC 00/11] DAX fsynx/msync support Dave Chinner <david@fromorbit.com> - 2015-11-02 21:20 +0100
      Re: [RFC 00/11] DAX fsynx/msync support Jeff Moyer <jmoyer@redhat.com> - 2015-11-02 22:10 +0100
        Re: [RFC 00/11] DAX fsynx/msync support Jeff Moyer <jmoyer@redhat.com> - 2015-11-04 19:40 +0100
        Re: [RFC 00/11] DAX fsynx/msync support Dave Chinner <david@fromorbit.com> - 2015-11-05 09:40 +0100
          Re: [RFC 00/11] DAX fsynx/msync support Jeff Moyer <jmoyer@redhat.com> - 2015-11-05 20:50 +0100
          Re: [RFC 00/11] DAX fsynx/msync support Jens Axboe <axboe@kernel.dk> - 2015-11-05 22:00 +0100

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