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 <almasrymina@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: Sandipan Das <sandipan@linux.ibm.com>	[powerpc64]
Acked-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Sandipan Das <sandipan@linux.ibm.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Shuah Khan <shuah@kernel.org>
Link: http://lkml.kernel.org/r/20200211213128.73302-8-almasrymina@google.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

tools/testing/selftests/vm/.gitignore

@@ -14,3 +14,4 @@ virtual_address_range
 gup_benchmark
 va_128TBswitch
 map_fixed_noreplace
+write_to_hugetlbfs

tools/testing/selftests/vm/Makefile

@@ -23,6 +23,7 @@ TEST_GEN_FILES += userfaultfd
 ifneq (,$(filter $(ARCH),arm64 ia64 mips64 parisc64 ppc64 riscv64 s390x sh64 sparc64 x86_64))
 TEST_GEN_FILES += va_128TBswitch
 TEST_GEN_FILES += virtual_address_range
+TEST_GEN_FILES += write_to_hugetlbfs
 endif
 
 TEST_PROGS := run_vmtests