HMM has gone through many revisions so far and still not accepted (or proposed for that matter) for the mainline Linux kernel. The newest HMM addition is anonymous memory migration support.
Links:
[1] http://www.tuxmachines.org/taxonomy/term/63
[2] http://www.phoronix.com/scan.php?page=news_item&px=HMM-Anonymous-Memory-Mig