On Tue, Oct 26, 2021 at 10:12:17PM +0800, 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. Yes, that was an intentional change to all three filesystems to make the steps we expose to sysadmins/users consistent and documented officially: https://lore.kernel.org/linux-fsdevel/20200429043328.411431-1-ira.weiny@xxxxxxxxx/ (This was the first step; ext* were converted as separate series around the same time.) --D > > > [1] https://lore.kernel.org/all/YW2Oj4FrIB8do3zX@xxxxxxxxxx/T/ > [2] > https://lore.kernel.org/all/YW2Oj4FrIB8do3zX@xxxxxxxxxx/T/#mf067498887ca2023c64c8b8f6aec879557eb28f8 > [3] 9cb20f94afcd2964944f9468e38da736ee855b19 ("fs/ext4: Make DAX mount > option a tri-state") > [4] 02beb2686ff964884756c581d513e103542dcc6a ("fs/xfs: Make DAX mount > option a tri-state") > > > -- > Thanks, > Jeffle
