Re: [PATCH 0/9] add ext4 per-inode DAX flag

From	Dan Williams <dan.j.williams@intel.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH 0/9] add ext4 per-inode DAX flag
Date	2017-09-07 23:00 +0200
Message-ID	<unc41-5dW-19@gated-at.bofh.it> (permalink)
References	<umuFH-AY-3@gated-at.bofh.it> <umy6C-38F-3@gated-at.bofh.it> <umLZU-4KN-17@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Wed, Sep 6, 2017 at 10:07 AM, Ross Zwisler
<ross.zwisler@linux.intel.com> wrote:
> On Tue, Sep 05, 2017 at 09:12:35PM -0500, Eric Sandeen wrote:
>> On 9/5/17 5:35 PM, Ross Zwisler wrote:
>> > The original intent of this series was to add a per-inode DAX flag to ext4
>> > so that it would be consistent with XFS.  In my travels I found and fixed
>> > several related issues in both ext4 and XFS.
>>
>> Hi Ross -
>>
>> hch had a lot of reasons to nuke the dax flag from orbit, and we just
>> /disabled/ it in xfs due to its habit of crashing the kernel...
>
> Ah, sorry, I wasn't CC'd on those threads and missed them.  For any interested
> bystanders:
>
> https://www.spinics.net/lists/linux-ext4/msg57840.html
> https://www.spinics.net/lists/linux-xfs/msg09831.html
> https://www.spinics.net/lists/linux-xfs/msg10124.html
>
>> so a couple questions:
>>
>> 1) does this series pass hch's "test the per-inode DAX flag" fstest?
>
> Nope, it has the exact same problems as the XFS per-inode DAX flag.
>
>> 2) do we have an agreement that we need this flag at all, or is this
>>    just a parity item because xfs has^whad a per-inode flag?
>
> It was for parity, and because it allows admins finer grained control over
> their system.  Basically all things discussed in response to Lukas's original
> patch in the first link above.

I think it's more than parity. When pmem is slower than page cache it
is actively harmful to have DAX enabled globally for a filesystem. So,
not only should we push for per-inode DAX control, we should also push
to deprecate the mount option. I agree with Christoph that we should
try to automatically and transparently enable DAX where it makes
sense, but we also need a finer-grained mechanism than a mount flag to
force the behavior one way or the other.

Thread

[PATCH 0/9] add ext4 per-inode DAX flag Ross Zwisler <ross.zwisler@linux.intel.com> - 2017-09-06 00:40 +0200
  [PATCH 9/9] ext4: add per-inode DAX flag Ross Zwisler <ross.zwisler@linux.intel.com> - 2017-09-06 00:40 +0200
  [PATCH 2/9] xfs: always use DAX if mount option is used Ross Zwisler <ross.zwisler@linux.intel.com> - 2017-09-06 00:40 +0200
  [PATCH 4/9] ext4: add ext4_should_use_dax() Ross Zwisler <ross.zwisler@linux.intel.com> - 2017-09-06 00:40 +0200
  [PATCH 8/9] ext4: add sanity check for encryption + DAX Ross Zwisler <ross.zwisler@linux.intel.com> - 2017-09-06 00:40 +0200
  [PATCH 5/9] ext4: ext4_change_inode_journal_flag error handling Ross Zwisler <ross.zwisler@linux.intel.com> - 2017-09-06 00:40 +0200
  [PATCH 7/9] ext4: prevent data corruption with inline data + DAX Ross Zwisler <ross.zwisler@linux.intel.com> - 2017-09-06 00:40 +0200
    Re: [PATCH 7/9] ext4: prevent data corruption with inline data + DAX Andreas Dilger <adilger@dilger.ca> - 2017-09-06 23:00 +0200
      Re: [PATCH 7/9] ext4: prevent data corruption with inline data + DAX Ross Zwisler <ross.zwisler@linux.intel.com> - 2017-09-07 01:20 +0200
  [PATCH 1/9] ext4: remove duplicate extended attributes defs Ross Zwisler <ross.zwisler@linux.intel.com> - 2017-09-06 00:40 +0200
    Re: [PATCH 1/9] ext4: remove duplicate extended attributes defs Jan Kara <jack@suse.cz> - 2017-09-06 09:30 +0200
  [PATCH 6/9] ext4: safely transition S_DAX on journaling changes Ross Zwisler <ross.zwisler@linux.intel.com> - 2017-09-06 00:40 +0200
    Re: [PATCH 6/9] ext4: safely transition S_DAX on journaling changes Jan Kara <jack@suse.cz> - 2017-09-06 11:50 +0200
      Re: [PATCH 6/9] ext4: safely transition S_DAX on journaling changes Ross Zwisler <ross.zwisler@linux.intel.com> - 2017-09-06 19:10 +0200
  Re: [PATCH 0/9] add ext4 per-inode DAX flag Eric Sandeen <esandeen@redhat.com> - 2017-09-06 04:20 +0200
    Re: [PATCH 0/9] add ext4 per-inode DAX flag Ross Zwisler <ross.zwisler@linux.intel.com> - 2017-09-06 19:10 +0200
      Re: [PATCH 0/9] add ext4 per-inode DAX flag Dan Williams <dan.j.williams@intel.com> - 2017-09-07 23:00 +0200
        Re: [PATCH 0/9] add ext4 per-inode DAX flag Ross Zwisler <ross.zwisler@linux.intel.com> - 2017-09-07 23:20 +0200
          Re: [PATCH 0/9] add ext4 per-inode DAX flag Andreas Dilger <adilger@dilger.ca> - 2017-09-07 23:30 +0200
            Re: [PATCH 0/9] add ext4 per-inode DAX flag Ross Zwisler <ross.zwisler@linux.intel.com> - 2017-09-08 00:00 +0200
              Re: [PATCH 0/9] add ext4 per-inode DAX flag Ross Zwisler <ross.zwisler@linux.intel.com> - 2017-09-08 00:20 +0200
                Re: [PATCH 0/9] add ext4 per-inode DAX flag Dave Chinner <david@fromorbit.com> - 2017-09-08 01:30 +0200
                Re: [PATCH 0/9] add ext4 per-inode DAX flag Jan Kara <jack@suse.cz> - 2017-09-08 11:50 +0200
                Re: [PATCH 0/9] add ext4 per-inode DAX flag Theodore Ts'o <tytso@mit.edu> - 2017-09-08 17:40 +0200
              Re: [PATCH 0/9] add ext4 per-inode DAX flag Dave Chinner <david@fromorbit.com> - 2017-09-08 00:20 +0200

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