Groups > linux.kernel > #1203642

Re: [PATCH v9 6/6] block: loop: support DIO & AIO

From	Christoph Hellwig <hch@infradead.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH v9 6/6] block: loop: support DIO & AIO
Date	2015-08-09 15:50 +0200
Message-ID	<pVz97-7GV-3@gated-at.bofh.it> (permalink)
References	(1 earlier) <pUp2a-3HO-29@gated-at.bofh.it> <pUKzE-1p3-19@gated-at.bofh.it> <pULcm-2og-9@gated-at.bofh.it> <pVsAG-6A9-13@gated-at.bofh.it> <pVywp-6Xi-5@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Sun, Aug 09, 2015 at 09:04:32AM -0400, Ming Lei wrote:
> Now the logical block size of loop is 512byte, but the sector size of
> backing device may be 4K, so we can't do 512 byte algined direct
> I/O to the filesystem in this situation.
> 
> With runtime switch to buffered I/O we can fix this problem, but
> most of times it won't fall in this case.

The right way to handle this case is to not allow direct I/O at all,
you'll be constantly switching between direct and buffered I/O
otherwise, which is a bad idea.

> For non-512 byte sector size of backing device, it is needed as
> I described above.

If the backing device sector size is smaller than that of the loop
device you should not allow direct I/O as you will be switching forth
and back ue to the IO patterns all the time.
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Thread

[PATCH v9 0/6] block: loop: improve loop with AIO Ming Lei <ming.lei@canonical.com> - 2015-08-06 10:50 +0200
  [PATCH v9 6/6] block: loop: support DIO & AIO Ming Lei <ming.lei@canonical.com> - 2015-08-06 10:50 +0200
    Re: [PATCH v9 6/6] block: loop: support DIO & AIO Christoph Hellwig <hch@infradead.org> - 2015-08-07 09:50 +0200
      Re: [PATCH v9 6/6] block: loop: support DIO & AIO Ming Lei <ming.lei@canonical.com> - 2015-08-07 10:30 +0200
        Re: [PATCH v9 6/6] block: loop: support DIO & AIO Christoph Hellwig <hch@infradead.org> - 2015-08-09 08:50 +0200
          Re: [PATCH v9 6/6] block: loop: support DIO & AIO Ming Lei <ming.lei@canonical.com> - 2015-08-09 15:10 +0200
            Re: [PATCH v9 6/6] block: loop: support DIO & AIO Christoph Hellwig <hch@infradead.org> - 2015-08-09 15:50 +0200
              Re: [PATCH v9 6/6] block: loop: support DIO & AIO Ming Lei <ming.lei@canonical.com> - 2015-08-09 16:30 +0200
                Re: [PATCH v9 6/6] block: loop: support DIO & AIO Dave Chinner <david@fromorbit.com> - 2015-08-10 01:50 +0200
                Re: [PATCH v9 6/6] block: loop: support DIO & AIO Ming Lei <ming.lei@canonical.com> - 2015-08-10 05:00 +0200
                Re: [PATCH v9 6/6] block: loop: support DIO & AIO Christoph Hellwig <hch@infradead.org> - 2015-08-10 10:10 +0200
                Re: [PATCH v9 6/6] block: loop: support DIO & AIO Ming Lei <ming.lei@canonical.com> - 2015-08-10 16:40 +0200

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