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Date: Tue, 2 Jun 2020 09:16:33 +0800 From: Xiao Yang <yangx.jy@...fujitsu.com> To: Jan Kara <jack@...e.cz> CC: Ira Weiny <ira.weiny@...el.com>, <linux-ext4@...r.kernel.org>, Andreas Dilger <adilger.kernel@...ger.ca>, "Theodore Y. Ts'o" <tytso@....edu>, Eric Biggers <ebiggers@...nel.org>, Al Viro <viro@...iv.linux.org.uk>, Dan Williams <dan.j.williams@...el.com>, Dave Chinner <david@...morbit.com>, Christoph Hellwig <hch@....de>, Jeff Moyer <jmoyer@...hat.com>, "Darrick J. Wong" <darrick.wong@...cle.com>, <linux-fsdevel@...r.kernel.org>, <linux-kernel@...r.kernel.org> Subject: Re: [PATCH V4 6/8] fs/ext4: Make DAX mount option a tri-state On 2020/5/28 17:41, Jan Kara wrote: > On Thu 28-05-20 16:56:51, Xiao Yang wrote: >> On 2020/5/28 7:50, Ira Weiny wrote: >>> On Wed, May 27, 2020 at 01:54:54PM +0800, Xiao Yang wrote: >>>> On 2020/5/22 3:13, ira.weiny@...el.com wrote: >>>>> From: Ira Weiny<ira.weiny@...el.com> >>>>> >>>>> We add 'always', 'never', and 'inode' (default). '-o dax' continues to >>>>> operate the same which is equivalent to 'always'. This new >>>>> functionality is limited to ext4 only. >>>>> >>>>> Specifically we introduce a 2nd DAX mount flag EXT4_MOUNT2_DAX_NEVER and set >>>>> it and EXT4_MOUNT_DAX_ALWAYS appropriately for the mode. >>>>> >>>>> We also force EXT4_MOUNT2_DAX_NEVER if !CONFIG_FS_DAX. >>>>> >>>>> Finally, EXT4_MOUNT2_DAX_INODE is used solely to detect if the user >>>>> specified that option for printing. >>>> Hi Ira, >>>> >>>> I have two questions when reviewing this patch: >>>> 1) After doing mount with the same dax=inode option, ext4/xfs shows >>>> differnt output(i.e. xfs doesn't print 'dax=inode'): >>>> --------------------------------------------------- >>>> # mount -o dax=inode /dev/pmem0 /mnt/xfstests/test/ >>>> # mount | grep pmem0 >>>> /dev/pmem0 on /mnt/xfstests/test type ext4 (rw,relatime,seclabel,dax=inode) >>>> >>>> # mount -odax=inode /dev/pmem1 /mnt/xfstests/scratch/ >>>> # mount | grep pmem1 >>>> /dev/pmem1 on /mnt/xfstests/scratch type xfs >>>> (rw,relatime,seclabel,attr2,inode64,logbufs=8,logbsize=32k,noquota) >>>> ---------------------------------------------------- >>>> Is this expected output? why don't unify the output? >>> >>> Correct. dax=inode is the default. xfs treats that default the same whether >>> you specify it on the command line or not. >>> >>> For ext4 Jan specifically asked that if the user specified dax=inode on the >>> command line that it be printed on the mount options. If you don't specify >>> anything then dax=inode is in effect but ext4 will not print anything. >>> >>> I had the behavior the same as XFS originally but Jan wanted it this way. The >>> XFS behavior is IMO better and is what the new mount infrastructure gives by >>> default. >> >> Could we unify the output? It is strange for me to use differnt output on >> ext4 and xfs. > > If we'd unify the output with XFS, it would be inconsistent with all the > other ext4 mount options. So I disagree with that. I agree it is not ideal > to have different behavior between xfs and ext4 but such is the historical > behavior. If we want to change that, we need to change the handling for all > the ext4 mount options. I'm open for that discussion but it is a problem > unrelated to this patch set. Hi Jan, Thanks for your quick feedback. Of course, this doubt should not block the patch set. Best Regards, Xiao Yang > > Honza
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