From: Andi Kleen <ak@suse.de>

Add support to tmpfs and hugetlbfs to support NUMA API.  Shared memory is a
bit of a special case for NUMA policy.  Normally policy is associated to VMAs
or to processes, but for a shared memory segment you really want to share the
policy.  The core NUMA API has code for that, this patch adds the necessary
changes to tmpfs and hugetlbfs.

First it changes the custom swapping code in tmpfs to follow the policy set
via VMAs.

It is also useful to have a "backing store" of policy that saves the policy
even when nobody has the shared memory segment mapped.  This allows command
line tools to pre configure policy, which is then later used by programs.

Note that hugetlbfs needs more changes - it is also required to switch it to
lazy allocation, otherwise the prefault prevents mbind() from working.