selftests: vm: add a hugetlb test case

selftests: vm: add a hugetlb test case

Since the head vmemmap page frame associated with each HugeTLB page is
reused, we should hide the PG_head flag of tail struct page from the user.
Add a tese case to check whether it is work properly.  The test steps are
as follows.

  1) alloc 2MB hugeTLB
  2) get each page frame
  3) apply those APIs in each page frame
  4) Those APIs work completely the same as before.

Reading the flags of a page by /proc/kpageflags is done in
stable_page_flags(), which has invoked PageHead(), PageTail(),
PageCompound() and compound_head().  If those APIs work properly, the head
page must have 15 and 17 bits set.  And tail pages must have 16 and 17
bits set but 15 bit unset.  Those flags are checked in check_page_flags().

Link: https://lkml.kernel.org/r/20211101031651.75851-5-songmuchun@bytedance.com
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Reviewed-by: Barry Song <song.bao.hua@hisilicon.com>
Cc: Bodeddula Balasubramaniam <bodeddub@amazon.com>
Cc: Chen Huang <chenhuang5@huawei.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Fam Zheng <fam.zheng@bytedance.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Xiongchun Duan <duanxiongchun@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>