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From: Eric Sandeen <>
To: "Darrick J. Wong" <>,
	Eric Sandeen <>
Cc: xfs <>, Bill O'Donnell <>
Subject: Re: [PATCH] mkfs.xfs.8: clarify DAX-vs-reflink restrictions in the mkfs.xfs man page
Date: Fri, 27 Aug 2021 11:23:22 -0500	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <20210827154905.GP12640@magnolia>

On 8/27/21 10:49 AM, Darrick J. Wong wrote:
> On Fri, Aug 27, 2021 at 10:39:18AM -0500, Eric Sandeen wrote:
>> Now that we have the tristate dax mount options, it is possible
>> to enable DAX mode for non-reflinked files on a reflink-capable
>> filesystem.  Clarify this in the mkfs.xfs manpage.
>> Reported-by: Bill O'Donnell <>
>> Signed-off-by: Eric Sandeen <>
>> ---
>> diff --git a/man/man8/mkfs.xfs.8 b/man/man8/mkfs.xfs.8
>> index a7f70285..84ac50e8 100644
>> --- a/man/man8/mkfs.xfs.8
>> +++ b/man/man8/mkfs.xfs.8
>> @@ -316,12 +316,20 @@ option set. When the option
>>   is used, the reference count btree feature is not supported and reflink is
>>   disabled.
>>   .IP
>> -Note: the filesystem DAX mount option (
>> +Note: the filesystem-wide DAX mount options (
>>   .B \-o dax
>> -) is incompatible with
>> -reflink-enabled XFS filesystems.  To use filesystem DAX with XFS, specify the
>> +and
>> +.B \-o dax=always
>> +) are incompatible with
>> +reflink-enabled XFS filesystems.  To use filesystem-wide DAX with XFS, specify the
>>   .B \-m reflink=0
>>   option to mkfs.xfs to disable the reflink feature.
>> +Alternatey, use the
> "Alternately..."


>> +.B \-o dax=inode
>> +mount option to selectively enable DAX mode on non-reflinked files.
> /me wonders if this is dangerously close to wading into the muck that is
> "Use dax=inode or even no dax option at all, then make sure nobody
> shares your file's data blocks to set the DAX fsxattr flag on the file,
> and /then/ you can have DAX."

Perhaps I should drop most of it, and just wave hands vaguely at xfs.5?


      reply	other threads:[~2021-08-27 16:23 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-27 15:39 [PATCH] mkfs.xfs.8: clarify DAX-vs-reflink restrictions in the mkfs.xfs man page Eric Sandeen
2021-08-27 15:46 ` Bill O'Donnell
2021-08-27 15:47   ` Eric Sandeen
2021-08-27 15:49 ` Darrick J. Wong
2021-08-27 16:23   ` Eric Sandeen [this message]

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