mm: add thp_size

This function returns the number of bytes in a THP.  It is like
page_size(), but compiles to just PAGE_SIZE if CONFIG_TRANSPARENT_HUGEPAGE
is disabled.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Link: http://lkml.kernel.org/r/20200629151959.15779-5-willy@infradead.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
index 719c352..e65629c0 100644
--- a/mm/page_vma_mapped.c
+++ b/mm/page_vma_mapped.c
@@ -227,7 +227,7 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
 			if (pvmw->address >= pvmw->vma->vm_end ||
 			    pvmw->address >=
 					__vma_address(pvmw->page, pvmw->vma) +
-					hpage_nr_pages(pvmw->page) * PAGE_SIZE)
+					thp_size(pvmw->page))
 				return not_found(pvmw);
 			/* Did we cross page table boundary? */
 			if (pvmw->address % PMD_SIZE == 0) {
@@ -268,7 +268,7 @@ int page_mapped_in_vma(struct page *page, struct vm_area_struct *vma)
 	unsigned long start, end;
 
 	start = __vma_address(page, vma);
-	end = start + PAGE_SIZE * (hpage_nr_pages(page) - 1);
+	end = start + thp_size(page) - PAGE_SIZE;
 
 	if (unlikely(end < vma->vm_start || start >= vma->vm_end))
 		return 0;