[$] The end of the DAX experiment

Since its inception, the DAX mechanism (which provides for direct access tofiles stored on persistent memory) has been seen as somewhat experimentaland incomplete. At the 2019 Linux Storage, Filesystem, andMemory-Management Summit, Dan Williams ran a session where he said thatperhaps the time has come to end that experiment. Some of theunimplemented DAX features may never actually need to be implemented, andit might just be possible to declare DAX finished. But first there are afew more details to take care of.