Improved EXT4 + XFS DAX Implementation Appears Ready To Go For Linux 5.8

Adding to the expected changes for Linux 5.8 is improved EXT4 and XFS file-system direct access "DAX" support.

DAX is the means of direct access to files backed by persistent memory (such as Intel Optane DC Persistent Memory) without needing to be copied via the page cache. Thus DAX bypasses that extra copy for reads/writes to the storage device and mapping the storage device directly into user-space.

In recent months have been patches for improving DAX on XFS and EXT4 to allow it to function on a per-file/directory basis with the global DAX mount option being too coarse for some use-cases.

Earlier in May those DAX improvements for XFS were queued and within the xfs-5.8-merge code.

In addition to the XFS code by Intel's Ira Weiny, the open-source developer has been similarly working on improved DAX support for EXT4 so that it can be done on a per-file/per-inode basis as well. The improved EXT4 DAX support has been going through a few rounds of review and this morning EXT4 maintainer Ted Ts'o has merged the improved DAX support into the EXT4 development code ahead of the imminent Linux 5.8 cycle.

The dax mount option for EXT4 and XFS now support enabling of "always", "never", or "inode" for the more selective handling.

More details on the refined direct access handling for EXT4 and XFS can be found via the updated documentation.