cc [Ira Weiny], author of per inode DAX on xfs/ext4 On 10/20/21 11:17 PM, Vivek Goyal wrote: > On Wed, Oct 20, 2021 at 10:52:38AM +0800, JeffleXu wrote: >> >> >> On 10/18/21 10:10 PM, Vivek Goyal wrote: >>> On Mon, Oct 11, 2021 at 11:00:47AM +0800, Jeffle Xu wrote: >>>> We add 'always', 'never', and 'inode' (default). '-o dax' continues to >>>> operate the same which is equivalent to 'always'. To be consistemt with >>>> ext4/xfs's tri-state mount option, when neither '-o dax' nor '-o dax=' >>>> option is specified, the default behaviour is equal to 'inode'. >>> >>> Hi Jeffle, >>> >>> I am not sure when -o "dax=inode" is used as a default? If user >>> specifies, "-o dax" then it is equal to "-o dax=always", otherwise >>> user will explicitly specify "-o dax=always/never/inode". So when >>> is dax=inode is used as default? >> >> That means when neither '-o dax' nor '-o dax=always/never/inode' is >> specified, it is actually equal to '-o dax=inode', which is also how >> per-file DAX on ext4/xfs works. > > [ CC dave chinner] > > Is it not change of default behavior for ext4/xfs as well. My > understanding is that prior to this new dax options, "-o dax" enabled > dax on filesystem and if user did not specify it, DAX is disbaled > by default. > > Now after introduction of "-o dax=always/never/inode", if suddenly > "-o dax=inode" became the default if user did not specify anything, > that's change of behavior. Is that intentional. If given a choice, > I would rather not change default and ask user to opt-in for > appropriate dax functionality. > > Dave, you might have thoughts on this. It makes me uncomfortable to > change virtiofs dax default now just because other filesytems did it. > I can only find the following discussions about the earliest record on this tri-state mount option: https://lore.kernel.org/lkml/20200316095509.GA13788@xxxxxx/ https://lore.kernel.org/lkml/20200401040021.GC56958@magnolia/ Hi, Ira Weiny, Do you have any thought on this, i.e. why the default behavior has changed after introduction of per inode dax? -- Thanks, Jeffle