[PATCH 5/6] Alter get_order() so that it can make use of long_log2() on a constant

David Howells
2006-09-13T13:03:09Z

From: David Howells <dhowells@redhat.com>

Alter get_order() so that it can make use of long_log2() on a constant to
produce a constant value, retaining the ability for an arch to override it in
the non-const case.

Signed-Off-By: David Howells <dhowells@redhat.com>
---

include/asm-generic/page.h | 14 -------------
include/linux/log2.h | 46 ++++++++++++++++++++++++++++++++++++++++++--
2 files changed, 44 insertions(+), 16 deletions(-)

diff --git a/include/asm-generic/page.h b/include/asm-generic/page.h
index a96b5d9..a7e374e 100644
--- a/include/asm-generic/page.h
+++ b/include/asm-generic/page.h
@@ -6,20 +6,6 @@ #ifndef __ASSEMBLY__

#include <linux/compiler.h>

-/* Pure 2^n version 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);
- return order;
-}
-
#endif /* __ASSEMBLY__ */
#endif /* __KERNEL__ */

diff --git a/include/linux/log2.h b/include/linux/log2.h
index 9bef055..a2f6858 100644
--- a/include/linux/log2.h
+++ b/include/linux/log2.h
@@ -1,4 +1,4 @@
-/* Log base 2 calculation
+/* Base 2 logarithm calculation stuff
*
* Copyright (C) 2006 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
@@ -25,6 +25,7 @@ int ____log2_NaN(void);
* non-constant log of base 2 calculation
* - the arch may override these in asm/bitops.h if they can be implemented
* more efficiently than using fls() and fls64()
+ * - the arch is not required to handle n==0 if implementing the fallback
*/
#ifndef ARCH_HAS_LOG2
static inline __attribute__((const))
@@ -43,6 +44,36 @@ int __ll_log2(u64 n)
#endif

/*
+ * non-const pure 2^n version of get_order
+ * - the arch may override these in asm/bitops.h if they can be implemented
+ * more efficiently than using the arch log2 routines
+ * - we use the non-const log2() instead if the arch has defined one suitable
+ */
+#ifndef ARCH_HAS_GET_ORDER
+static inline __attribute__((const))
+int __get_order(unsigned long size, int page_shift)
+{
+#if BITS_PER_LONG == 32 && defined(ARCH_HAS_LOG2)
+ int order = __log2(size) - page_shift;
+ return order >= 0 ? order : 0;
+#elif BITS_PER_LONG == 64 && defined(ARCH_HAS_LL_LOG2)
+ int order = __ll_log2(size) - page_shift;
+ return order >= 0 ? order : 0;
+#else
+ int order;
+
+ size = (size - 1) >> (page_shift - 1);
+ order = -1;
+ do {
+ size >>= 1;
+ order++;
+ } while (size);
+ return order;
+#endif
+}
+#endif
+
+/*
* constant-capable 32-bit log of base 2 calculation
* - this can be used to initialise global variables from constant data, hence
* the massive ternary operator construction
@@ -167,7 +198,7 @@ ( \
)

/*
- * constant-capable unsigned long log of base 2 calculation
+ * constant-capable log of base 2 calculation of unsigned long
* - this can be used to initialise global variables from constant data
*/
#if BITS_PER_LONG == 32
@@ -176,4 +207,15 @@ #else
#define long_log2(n) ll_log2(n)
#endif

+/*
+ * calculate allocation order based on the current page size
+ * - this can be used to initialise global variables from constant data
+ */
+#define get_order(n) \
+( \
+ __builtin_constant_p(n) ? \
+ ((n < (1UL << PAGE_SHIFT)) ? 0 : long_log2(n) - PAGE_SHIFT) : \
+ __get_order(n, PAGE_SHIFT) \
+ )
+
#endif /* _LINUX_LOG2_H */