Re: [PATCH 1/7] xfs: always use DAX if mount option is used

From	Christoph Hellwig <hch@lst.de>
Newsgroups	linux.kernel
Subject	Re: [PATCH 1/7] xfs: always use DAX if mount option is used
Date	2017-09-26 16:40 +0200
Message-ID	<utZbH-5XL-1@gated-at.bofh.it> (permalink)
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On Tue, Sep 26, 2017 at 09:09:57PM +1000, Dave Chinner wrote:
> Well, quite frankly, I never wanted the mount option for XFS. It was
> supposed to be for initial testing only, then we'd /always/ use the
> the inode flags. For a filesystem to default to using DAX, we
> set the DAX flag on the root inode at mkfs time, and then everything
> inode flag based just works.

And I deeply fundamentally disagree.  The mount option is a nice
enough big hammer to try a mode without encoding nitty gritty details
into the application ABI.

The per-inode persistent flag is the biggest nightmare ever, as we see
in all these discussions about it.

What does it even mean?  Right now it forces direct addressing as long
as the underlying media supports that.  But what about media that
you directly access but you really don't want to because it's really slow?
Or media that is so god damn fast that you never want to buffer?  Or
media where you want to buffer for writes (or at least some of them)
but not for reads?

It encodes a very specific mechanism for an early direct access
implementation into the ABI.  What we really need is for applications
to declare an intent, not specify a particular mechanism.

Thread

[PATCH 1/7] xfs: always use DAX if mount option is used Ross Zwisler <ross.zwisler@linux.intel.com> - 2017-09-26 01:20 +0200
  Re: [PATCH 1/7] xfs: always use DAX if mount option is used Dave Chinner <david@fromorbit.com> - 2017-09-26 02:30 +0200
    Re: [PATCH 1/7] xfs: always use DAX if mount option is used Jan Kara <jack@suse.cz> - 2017-09-26 11:40 +0200
      Re: [PATCH 1/7] xfs: always use DAX if mount option is used Dave Chinner <david@fromorbit.com> - 2017-09-26 13:20 +0200
        Re: [PATCH 1/7] xfs: always use DAX if mount option is used Christoph Hellwig <hch@lst.de> - 2017-09-26 16:40 +0200
          Re: [PATCH 1/7] xfs: always use DAX if mount option is used Ross Zwisler <ross.zwisler@linux.intel.com> - 2017-09-26 19:40 +0200
            Re: [PATCH 1/7] xfs: always use DAX if mount option is used "Darrick J. Wong" <darrick.wong@oracle.com> - 2017-09-26 22:00 +0200
              Re: [PATCH 1/7] xfs: always use DAX if mount option is used Dave Chinner <david@fromorbit.com> - 2017-09-27 00:10 +0200
            Re: [PATCH 1/7] xfs: always use DAX if mount option is used Christoph Hellwig <hch@infradead.org> - 2017-09-27 08:50 +0200
              Re: [PATCH 1/7] xfs: always use DAX if mount option is used Ross Zwisler <ross.zwisler@linux.intel.com> - 2017-09-27 18:20 +0200
                Re: [PATCH 1/7] xfs: always use DAX if mount option is used Christoph Hellwig <hch@lst.de> - 2017-10-01 10:20 +0200
        Re: [PATCH 1/7] xfs: always use DAX if mount option is used Eric Sandeen <sandeen@sandeen.net> - 2017-09-26 20:10 +0200
    Re: [PATCH 1/7] xfs: always use DAX if mount option is used Ross Zwisler <ross.zwisler@linux.intel.com> - 2017-09-26 21:00 +0200

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