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-rw-r--r--include/asm-generic/getorder.h53
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 */
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