On Wed, Feb 12, 2020 at 02:49:48PM -0500, Jeff Moyer wrote: > Ira Weiny <ira.weiny@xxxxxxxxx> writes: > > > On Mon, Feb 10, 2020 at 10:15:47AM -0500, Jeff Moyer wrote: > >> Hi, Ira, > >> > >> Could you please include documentation patches as part of this series? > > > > I do have an update to the vfs.rst doc in > > > > fs: Add locking for a dynamic DAX state > > > > I'm happy to do more but was there something specific you would like to see? > > Or documentation in xfs perhaps? > > Sorry, I was referring to your statx man page addition. Ah yea I guess I could include that as a patch. I just wanted to get buy off on the whole thing prior to setting documentation in. > It would be > nice if we could find a home for the information in your cover letter, > too. Right now, I'm not sure how application developers are supposed to > figure out how to use the per-inode settings. I'm not sure either. But this is probably a good start: https://www.kernel.org/doc/Documentation/filesystems/dax.txt Something under the Usage section like: diff --git a/Documentation/filesystems/dax.txt b/Documentation/filesystems/dax.txt index 679729442fd2..1bab5d5d775b 100644 --- a/Documentation/filesystems/dax.txt +++ b/Documentation/filesystems/dax.txt @@ -20,8 +20,18 @@ Usage If you have a block device which supports DAX, you can make a filesystem on it as usual. The DAX code currently only supports files with a block size equal to your kernel's PAGE_SIZE, so you may need to specify a block -size when creating the filesystem. When mounting it, use the "-o dax" -option on the command line or add 'dax' to the options in /etc/fstab. +size when creating the filesystem. + +Files can then be enabled to use dax using the statx system call or an +application using it like 'xfs_io'. Directories can also be enabled for dax +to have the file system automatically enable dax on all files within those +directories. + +Alternately, when mounting it one can use the "-o dax" option on the command +line or add 'dax' to the options in /etc/fstab to globaly override all files to +use dax on that filesystem. Using the "-o dax" does not change the state of +individual files so remounting without "-o dax" will revert them to the state +saved in the filesystem meta data. Implementation Tips for Block Driver Writers > > If I read your cover letter correctly, the mount option overrides any > on-disk setting. Is that right? Yes > Given that we document the dax mount > option as "the way to get dax," it may be a good idea to allow for a > user to selectively disable dax, even when -o dax is specified. Is that > possible? Not with this patch set. And I'm not sure how that would work. The idea was that -o dax was simply an override for users who were used to having their entire FS be dax. We wanted to depreciate the use of "-o dax" in general. The individual settings are saved so I don't think it makes sense to ignore the -o dax in favor of those settings. Basically that would IMO make the -o dax useless. Ira
