linux-ext4 - Re: [PATCH 0/3] ext2, ext4, xfs: hard fail dax mount on unsupported devices

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Date:   Fri, 12 Oct 2018 10:21:54 +0200
From:   Christoph Hellwig <hch@....de>
To:     Eric Sandeen <sandeen@...deen.net>
Cc:     Dan Williams <dan.j.williams@...el.com>, Jan Kara <jack@...e.cz>,
        linux-xfs <linux-xfs@...r.kernel.org>,
        linux-ext4 <linux-ext4@...r.kernel.org>,
        Ross Zwisler <zwisler@...nel.org>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH 0/3] ext2, ext4, xfs: hard fail dax mount on
 unsupported devices

On Thu, Oct 11, 2018 at 01:38:34PM -0500, Eric Sandeen wrote:
> > The different behavior between filesystems was confusing customers so
> > we had to align them, then the question was which default to pick.
> > Honestly, we came to the decision to bring ext4 in line with the xfs
> > behavior because we thought that would be easier than the alternative.
> > Dave and Christoph made repeated arguments that DAX is just a hidden
> > performance optimization that no application should rely on, so we
> > went the path of least resistance and changed the ext4 default.
> 
> Ok, well, I guess we'd better reconcile "it's a hidden performance hint"
> with "if the administrator asked they must receive..." before making this
> change... cc: hch for bonus input.

I don't really care too mouch on the mount options, the important bit
was the application behavior.

I fully agree with Dan that we should have the same behavior for every
file system, though.