[RFC][ for -mm] memory cgroup enhancements take3 [0/9] intro

[KAMEZAWA Hiroyuki]

Hi, this is updated set of enhancements for memory cgroup in my box.
I'd like to post some of these when the next -mm is shipped.
(but rebase and more test should be done.)

Any comments are welcome.

Changes from previous sets:
 - added comments/explanation.
 - dropped failcnt patch
 - modified per-node numastat to zonestat
 - and small changes for good looking.

Thanks,
-Kame