[$] Two more approaches to persistent-memory writes

The persistent-memory arrays we're told we'll all be able to get somedaypromise high-speed, byte-addressable storage in massive quantities. TheLinux kernel community has been working to support thistechnology fully for a few years now, but there is one problem lacking a propersolution: allowing direct writes to persistent memory that is managed by afilesystem. None of the proposed solutions have yet madeit into the mainline, but that hasn't stopped developers from trying; nowtwo new patch sets addressing this issue are under consideration.