mmap() + checksum = ?

The approach that NOVA takes is to disable parity/checksum protection while data is mmap'd and re-enable it when the mapping is finished. We track overlapping maps etc., and we have log mmap operations so we can re-enable protection after reboot.

The reasoning for this approach is that when you use DAX-mmap() you take responsibility for your data. This includes responsibility for updating it consistently and responsibility for protecting it from media errors, etc. As you point out, the file system really can't fill this role (at least not without a significant performance penalty), so it must fall to the application.

-steve