+ unsigned long compound_head; /* If bit zero is set */
+
+ /* First tail page only */
+#ifdef CONFIG_64BIT
+ /*
+ * On 64 bit system we have enough space in struct page
+ * to encode compound_dtor and compound_order with
+ * unsigned int. It can help compiler generate better or
+ * smaller code on some archtectures.
+ */
+ unsigned int compound_dtor;
+ unsigned int compound_order;
+#else
+ unsigned short int compound_dtor;
+ unsigned short int compound_order;
+#endif