+
+/*
+ * When a memory allocation must conform to specific limitations (such
+ * as being suitable for DMA) the caller will pass in hints to the
+ * allocator in the gfp_mask, in the zone modifier bits. These bits
+ * are used to select a priority ordered list of memory zones which
+ * match the requested limits. GFP_ZONEMASK defines which bits within
+ * the gfp_mask should be considered as zone modifiers. Each valid
+ * combination of the zone modifier bits has a corresponding list
+ * of zones (in node_zonelists). Thus for two zone modifiers there
+ * will be a maximum of 4 (2 ** 2) zonelists, for 3 modifiers there will
+ * be 8 (2 ** 3) zonelists. GFP_ZONETYPES defines the number of possible
+ * combinations of zone modifiers in "zone modifier space".
+ *
+ * As an optimisation any zone modifier bits which are only valid when
+ * no other zone modifier bits are set (loners) should be placed in
+ * the highest order bits of this field. This allows us to reduce the
+ * extent of the zonelists thus saving space. For example in the case
+ * of three zone modifier bits, we could require up to eight zonelists.
+ * If the left most zone modifier is a "loner" then the highest valid
+ * zonelist would be four allowing us to allocate only five zonelists.
+ * Use the first form for GFP_ZONETYPES when the left most bit is not
+ * a "loner", otherwise use the second.
+ *
+ * NOTE! Make sure this matches the zones in <linux/gfp.h>
+ */
+#define GFP_ZONEMASK 0x07
+/* #define GFP_ZONETYPES (GFP_ZONEMASK + 1) */ /* Non-loner */
+#define GFP_ZONETYPES ((GFP_ZONEMASK + 1) / 2 + 1) /* Loner */