thp: introduce hugepage_vma_check()

thp: introduce hugepage_vma_check()

commit fa475e517adb422cb3492e636195f9b2c0d009c8 upstream.

Multiple places do the same check.

Signed-off-by: Bob Liu <lliubbo@gmail.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Minchan Kim <minchan.kim@gmail.com>
Cc: Ni zhan Chen <nizhan.chen@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[bwh: Backported to 3.2:
 - Also move the is_linear_pfn_mapping() test
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>