hugetlb_cgroup: add hugetlb_cgroup reservation tests

hugetlb_cgroup: add hugetlb_cgroup reservation tests

The tests use both shared and private mapped hugetlb memory, and monitors
the hugetlb usage counter as well as the hugetlb reservation counter.
They test different configurations such as hugetlb memory usage via
hugetlbfs, or MAP_HUGETLB, or shmget/shmat, and with and without
MAP_POPULATE.

Also add test for hugetlb reservation reparenting, since this is a subtle
issue.

Signed-off-by: Mina Almasry <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Tested-by: Sandipan Das <[email protected]>	[powerpc64]
Acked-by: Mike Kravetz <[email protected]>
Cc: Sandipan Das <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Greg Thelen <[email protected]>
Cc: Shakeel Butt <[email protected]>
Cc: Shuah Khan <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Linus Torvalds <[email protected]>