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Date:   Wed, 27 Oct 2021 10:52:42 +0800
From:   JeffleXu <>
To:     Theodore Ts'o <>,,
        "Darrick J. Wong" <>,
        "" <>,,,
        Vivek Goyal <>, Christoph Hellwig <>
Subject: Re: [Question] ext4/xfs: Default behavior changed after per-file DAX

Sorry for the noise. Ira Weiny had replied my previous mail [1] but
unfortunately the reply was moved into junk box, and I didn't note that.


On 10/26/21 10:12 PM, JeffleXu wrote:
> Hi,
> Recently I'm working on supporting per-file DAX for virtiofs [1]. Vivek
> Goyal and I are interested [2] why the default behavior has changed
> since introduction of per-file DAX on ext4 and xfs [3][4].
> That is, before the introduction of per-file DAX, when user doesn't
> specify '-o dax', DAX is disabled for all files. After supporting
> per-file DAX, when neither '-o dax' nor '-o dax=always|inode|never' is
> specified, it actually works in a '-o dax=inode' way if the underlying
> blkdev is DAX capable, i.e. depending on the persistent inode flag. That
> is, the default behavior has changed from user's perspective.
> We are not sure if this is intentional or not. Appreciate if anyone
> could offer some hint.
> [1]
> [2]
> [3] 9cb20f94afcd2964944f9468e38da736ee855b19 ("fs/ext4: Make DAX mount
> option a tri-state")
> [4] 02beb2686ff964884756c581d513e103542dcc6a ("fs/xfs: Make DAX mount
> option a tri-state")


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