From: Andy Whitcroft <apw@shadowen.org>

Two problems:

a) The memory overcommit code fails oto take into account all the pages
   which are pinned by being reserved for the hugetlbpage pool

b) We're performing overcommit accounting and checking on behalf of
   hugetlbpage vmas.

The main thrust is to ensure that VM_ACCOUNT actually only gets set on
vma's which are indeed accountable.  With that ensured much of the rest
comes out in the wash.  It also removes the hugetlb memory for the
overcommit_memory=2 case.