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[PATCH] LOG2: Alter get_order() so that it can make use of ilog2() on a constant 

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>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
David Howells 2006-12-08 02:37:52 -08:00 committed by Linus Torvalds
parent 312a0c1709
commit 39d61db0ed
1 changed files with 34 additions and 4 deletions
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38
include/asm-generic/page.h
View File

@ -4,21 +4,51 @@
#ifdef __KERNEL__
#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)
/*
* 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);
size = (size - 1) >> (page_shift - 1);
order = -1;
do {
size >>= 1;
order++;
} while (size);
return order;
#endif
}
#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 /* __ASSEMBLY__ */
#endif /* __KERNEL__ */