hugetlb: quota is not freed for unused reserved private huge pages

hugetlb: quota is not freed for unused reserved private huge pages

With shared reservations (and now also with private reservations), we reserve
huge pages at mmap time.  We also account for the mapping against fs quota to
prevent a reservation from being preempted by quota exhaustion.

When testing with the libhugetlbfs test suite, I found a problem with quota
accounting.  FS quota for allocated pages is handled correctly but we are not
releasing quota for private pages that were reserved but never allocated.  Do
this in hugetlb_vm_op_close() at the same time as unused page reservations are
released.

Signed-off-by: Adam Litke <agl@us.ibm.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Johannes Weiner <hannes@saeurebad.de>
Cc: William Lee Irwin III <wli@holomorphy.com>
Cc: Hugh Dickins <hugh@veritas.com>
Acked-by: Andy Whitcroft <apw@shadowen.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>