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Subject[PATCH 5/7] Alter get_order() so that it can make use of ilog2() on a constant [try #2]
Date
From: David Howells <dhowells@redhat.com>

Alter get_order() so that it can make use of ilog2() 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 | 45 ++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 45 insertions(+), 14 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 6ce81b7..88b7b0e 100644
--- a/include/linux/log2.h
+++ b/include/linux/log2.h
@@ -25,6 +25,7 @@ int ____ilog2_NaN(void);
* non-constant log of base 2 calculators
* - 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_ILOG2_U32
static inline __attribute__((const))
@@ -42,6 +43,36 @@ int __ilog2_u64(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_ILOG2_U32)
+ int order = __ilog2_u32(size) - page_shift;
+ return order >= 0 ? order : 0;
+#elif BITS_PER_LONG == 64 && defined(ARCH_HAS_ILOG2_U64)
+ int order = __ilog2_u64(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
+
/**
* ilog2_u32 - log of base 2 of 32-bit unsigned value
* @n - parameter
@@ -185,4 +216,18 @@ #else
#define ilog2(n) ilog2_u64(n)
#endif

+/**
+ * get_order - calculate log2(pages) to hold a block of the specified size
+ * @n - size
+ *
+ * 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 : ilog2(n) - PAGE_SHIFT) : \
+ __get_order(n, PAGE_SHIFT) \
+ )
+
#endif /* _LINUX_LOG2_H */
-
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