I thought you might be interested in some performance results, "hot off the presses".
With DAX enabled, I see the following messages in the guest kernel logs, which I assume means it is working: [ 0.469364] EXT4-fs (pmem0): DAX enabled. Warning: EXPERIMENTAL, use at your own risk [ 0.469932] EXT4-fs (pmem0): mounting ext2 file system using the ext4 subsystem [ 0.470682] EXT4-fs (pmem0): mounted filesystem without journal. Opts: dax Enabling vNVDIMM + ext4.ko + DAX for the libguestfs appliance[1] root disk improves our boot+shutdown performance measure[2] by between 20 and 30 milliseconds, which is about 5% faster at the moment. I also wanted to know if memory usage is reduced. I ran `free -m' inside a freshly booted appliance. Without DAX: $ free -m total used free shared buff/cache available Mem: 485 3 451 1 30 465 Swap: 0 0 0 With DAX: $ free -m total used free shared buff/cache available Mem: 485 3 469 1 12 467 Swap: 0 0 0 I also wanted to know if qemu's memory usage is reduced. I captured the rusage.ru_maxrss of the qemu subprocess with and without DAX. The difference is only about 5 MB, which doesn't seem like very much to me. Perhaps I'm measuring this wrong. If you have better suggestions for measuring memory usage, please let me know. Rich. [1] http://libguestfs.org/guestfs-internals.1.html#architecture [2] http://libguestfs.org/guestfs-performance.1.html#baseline:-starting-the-appliance -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com Fedora Windows cross-compiler. Compile Windows programs, test, and build Windows installers. Over 100 libraries supported. http://fedoraproject.org/wiki/MinGW