+		 * If pmd isn't transhuge but the page is THP and
+		 * is owned by only this process, split it and
+		 * deactivate all pages.
+		 */
+		if (PageTransCompound(page)) {
+			if (page_mapcount(page) != 1)
+				goto out;
+			get_page(page);
+			if (!trylock_page(page)) {
+				put_page(page);
+				goto out;
+			}
+			pte_unmap_unlock(orig_pte, ptl);
+			if (split_huge_page(page)) {
+				unlock_page(page);
+				put_page(page);
+				pte_offset_map_lock(mm, pmd, addr, &ptl);
+				goto out;
+			}
+			pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
+			pte--;
+			addr -= PAGE_SIZE;
+			continue;
+		}

looks like this leaks page count if split_huge_page() is succesfull
(returns zero).

--Mika