EXT4 Per-Inode DAX Support Sent In As A Last Minute Linux 5.8 Addition

Hours ahead of the expected Linux 5.8-rc1 release that also marks the merge window closure of new features for this next kernel version, a secondary EXT4 file-system set of changes were just mailed in.

Ted Ts'o sent in this last minute pull request as first he was waiting on the necessary DAX infrastructure bits to land as part of the XFS pull request and wrapping up some regression/bug fixes. The main feature of this pull is enabling per-inode DAX support for EXT4, similar to the XFS functionality that came this window as well.

This is the work I covered on Phoronix last month with Improved EXT4 + XFS DAX Implementation Appears Ready To Go For Linux 5.8. The per-inode DAX support allows enabling the direct access functionality on a per-file/directory basis rather than globally for a given file-system. This more fine grained DAX control has been sought after by the likes of those using Intel Optane DC Persistent Memory. For those wanting the global behavior of DAX, it still can be set as such via the modified DAX mount option.

The per-inode DAX support for EXT4 is the main focus of this pull request. It was just sent out and hasn't landed yet but should still ahead of the upcoming 5.8-rc1 release.

See the tentative Linux 5.8 feature overview for other changes coming with this kernel release.