1 files changed, 45 insertions, 8 deletions

diff --git a/include/asm-generic/getorder.h b/include/asm-generic/getorder.h
index 67e7245dc9b3..65e4468ac53d 100644
--- a/include/asm-generic/getorder.h
+++ b/include/asm-generic/getorder.h
@@ -4,21 +4,58 @@
 #ifndef __ASSEMBLY__
 
 #include <linux/compiler.h>
+#include <linux/log2.h>
 
-/* Pure 2^n version of get_order */
-static inline __attribute_const__ int get_order(unsigned long size)
+/*
+ * Runtime evaluation of get_order()
+ */
+static inline __attribute_const__
+int __get_order(unsigned long size)
 {
         int order;
 
-        size = (size - 1) >> (PAGE_SHIFT - 1);
-        order = -1;
-        do {
-                size >>= 1;
-                order++;
-        } while (size);
+        size--;
+        size >>= PAGE_SHIFT;
+#if BITS_PER_LONG == 32
+        order = fls(size);
+#else
+        order = fls64(size);
+#endif
         return order;
 }
 
+/**
+ * get_order - Determine the allocation order of a memory size
+ * @size: The size for which to get the order
+ *
+ * Determine the allocation order of a particular sized block of memory.  This
+ * is on a logarithmic scale, where:
+ *
+ *      0 -> 2^0 * PAGE_SIZE and below
+ *      1 -> 2^1 * PAGE_SIZE to 2^0 * PAGE_SIZE + 1
+ *      2 -> 2^2 * PAGE_SIZE to 2^1 * PAGE_SIZE + 1
+ *      3 -> 2^3 * PAGE_SIZE to 2^2 * PAGE_SIZE + 1
+ *      4 -> 2^4 * PAGE_SIZE to 2^3 * PAGE_SIZE + 1
+ *      ...
+ *
+ * The order returned is used to find the smallest allocation granule required
+ * to hold an object of the specified size.
+ *
+ * The result is undefined if the size is 0.
+ *
+ * This function may be used to initialise variables with compile time
+ * evaluations of constants.
+ */
+#define get_order(n)                                            \
+(                                                               \
+        __builtin_constant_p(n) ? (                             \
+                ((n) == 0UL) ? BITS_PER_LONG - PAGE_SHIFT :     \
+                (((n) < (1UL << PAGE_SHIFT)) ? 0 :              \
+                 ilog2((n) - 1) - PAGE_SHIFT + 1)               \
+        ) :                                                     \
+        __get_order(n)                                          \
+)
+
 #endif  /* __ASSEMBLY__ */
 
 #endif  /* __ASM_GENERIC_GETORDER_H */