+
+/*
+ * 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".
+ */