- if ((flags & (__GFP_HIGHMEM | __GFP_MOVABLE)) ==
- (__GFP_HIGHMEM | __GFP_MOVABLE))
- return base + ZONE_MOVABLE;
-#ifdef CONFIG_HIGHMEM
- if (flags & __GFP_HIGHMEM)
- return base + ZONE_HIGHMEM;
+
+/*
+ * GFP_ZONE_TABLE is a word size bitstring that is used for looking up the
+ * zone to use given the lowest 4 bits of gfp_t. Entries are ZONE_SHIFT long
+ * and there are 16 of them to cover all possible combinations of
+ * __GFP_DMA, __GFP_DMA32, __GFP_MOVABLE and __GFP_HIGHMEM.
+ *
+ * The zone fallback order is MOVABLE=>HIGHMEM=>NORMAL=>DMA32=>DMA.
+ * But GFP_MOVABLE is not only a zone specifier but also an allocation
+ * policy. Therefore __GFP_MOVABLE plus another zone selector is valid.
+ * Only 1 bit of the lowest 3 bits (DMA,DMA32,HIGHMEM) can be set to "1".
+ *
+ * bit result
+ * =================
+ * 0x0 => NORMAL
+ * 0x1 => DMA or NORMAL
+ * 0x2 => HIGHMEM or NORMAL
+ * 0x3 => BAD (DMA+HIGHMEM)
+ * 0x4 => DMA32 or DMA or NORMAL
+ * 0x5 => BAD (DMA+DMA32)
+ * 0x6 => BAD (HIGHMEM+DMA32)
+ * 0x7 => BAD (HIGHMEM+DMA32+DMA)
+ * 0x8 => NORMAL (MOVABLE+0)
+ * 0x9 => DMA or NORMAL (MOVABLE+DMA)
+ * 0xa => MOVABLE (Movable is valid only if HIGHMEM is set too)
+ * 0xb => BAD (MOVABLE+HIGHMEM+DMA)
+ * 0xc => DMA32 (MOVABLE+HIGHMEM+DMA32)
+ * 0xd => BAD (MOVABLE+DMA32+DMA)
+ * 0xe => BAD (MOVABLE+DMA32+HIGHMEM)
+ * 0xf => BAD (MOVABLE+DMA32+HIGHMEM+DMA)
+ *
+ * ZONES_SHIFT must be <= 2 on 32 bit platforms.
+ */
+
+#if 16 * ZONES_SHIFT > BITS_PER_LONG
+#error ZONES_SHIFT too large to create GFP_ZONE_TABLE integer