huge_page_release()             -- hugepage refcounting
free_huge_page()                -- separates freeing from inode refcounting
unmap_hugepage_range()          -- unmapping refcounting hook when locked
zap_hugepage_range()            -- unmappping refcounting hook when unlocked
export setattr_mask()           -- hugetlbfs wants to call it
export destroy_inode()          -- hugetlbfs wants to use it
export unmap_vma()              -- hugetlbpage.c wants to use it
unlock_page() in hugetlbpage.c  -- fixes deadlock in hugetlbfs_truncate()