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] 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
