mm/huge_memory.c: add missing read-only THP checking in transparent_hugepage_enabled()

mm/huge_memory.c: add missing read-only THP checking in transparent_hugepage_enabled()

Since commit 99cb0dbd47a1 ("mm,thp: add read-only THP support for
(non-shmem) FS"), read-only THP file mapping is supported.  But it forgot
to add checking for it in transparent_hugepage_enabled().  To fix it, we
add checking for read-only THP file mapping and also introduce helper
transhuge_vma_enabled() to check whether thp is enabled for specified vma
to reduce duplicated code.  We rename transparent_hugepage_enabled to
transparent_hugepage_active to make the code easier to follow as suggested
by David Hildenbrand.

[[email protected]: define transhuge_vma_enabled next to transhuge_vma_suitable]
Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS")
Signed-off-by: Miaohe Lin <[email protected]>
Reviewed-by: Yang Shi <[email protected]>
Cc: Alexey Dobriyan <[email protected]>
Cc: "Aneesh Kumar K . V" <[email protected]>
Cc: Anshuman Khandual <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Kirill A. Shutemov <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: Ralph Campbell <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Song Liu <[email protected]>
Cc: William Kucharski <[email protected]>
Cc: Zi Yan <[email protected]>
Cc: Mike Kravetz <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>