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Message-Id: <1282217856-8625-1-git-send-email-namhyung@gmail.com>
Date: Thu, 19 Aug 2010 20:37:36 +0900
From: Namhyung Kim <namhyung@...il.com>
To: Arnd Bergmann <arnd@...db.de>, linux-arch@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
Subject: [RFC][PATCH] introduce ptr_diff()
When I compiled allyesconfig'ed kernel with C=1, I got 1519 lines of
following message:
include/linux/mm.h:599:16: warning: potentially expensive pointer subtraction
which is around 10% of total warnings. this was caused by page_to_pfn() macro
so I think it's worth to remove it by calculating pointer subtraction
manually.
ptr_diff() does subtraction of two pointers as if they were integer values
and divides it by the size of their base type. Currently it does not deal
with a difference alignment requirement than the size of base type, it
would be a trivial job.
Impact: remove a _lot_ of sparse warnings
Signed-off-by: Namhyung Kim <namhyung@...il.com>
---
I have no idea where the right place is.
Please kindly point me to the place if here is not the one.
And any comments are greatly welcomed also.
Thanks.
include/asm-generic/memory_model.h | 23 +++++++++++++++++++----
1 files changed, 19 insertions(+), 4 deletions(-)
diff --git a/include/asm-generic/memory_model.h b/include/asm-generic/memory_model.h
index fb2d63f..ffec625 100644
--- a/include/asm-generic/memory_model.h
+++ b/include/asm-generic/memory_model.h
@@ -22,13 +22,28 @@
#endif /* CONFIG_DISCONTIGMEM */
+#include <linux/log2.h>
+
+#define ptr_diff(p1, p2) \
+({ long __diff; \
+ unsigned long __addr1 = (unsigned long) (p1); \
+ unsigned long __addr2 = (unsigned long) (p2); \
+ unsigned __size = sizeof(typeof(*p1)); \
+ \
+ if (is_power_of_2(__size)) \
+ __diff = (__addr1 - __addr2) >> ilog2(__size); \
+ else \
+ __diff = (__addr1 - __addr2) / __size; \
+ __diff; \
+})
+
/*
* supports 3 memory models.
*/
#if defined(CONFIG_FLATMEM)
#define __pfn_to_page(pfn) (mem_map + ((pfn) - ARCH_PFN_OFFSET))
-#define __page_to_pfn(page) ((unsigned long)((page) - mem_map) + \
+#define __page_to_pfn(page) ((unsigned long)(ptr_diff((page), mem_map)) + \
ARCH_PFN_OFFSET)
#elif defined(CONFIG_DISCONTIGMEM)
@@ -41,7 +56,7 @@
#define __page_to_pfn(pg) \
({ struct page *__pg = (pg); \
struct pglist_data *__pgdat = NODE_DATA(page_to_nid(__pg)); \
- (unsigned long)(__pg - __pgdat->node_mem_map) + \
+ (unsigned long)(ptr_diff(__pg, __pgdat->node_mem_map)) + \
__pgdat->node_start_pfn; \
})
@@ -49,7 +64,7 @@
/* memmap is virtually contiguous. */
#define __pfn_to_page(pfn) (vmemmap + (pfn))
-#define __page_to_pfn(page) (unsigned long)((page) - vmemmap)
+#define __page_to_pfn(page) (unsigned long)(ptr_diff((page), vmemmap))
#elif defined(CONFIG_SPARSEMEM)
/*
@@ -59,7 +74,7 @@
#define __page_to_pfn(pg) \
({ struct page *__pg = (pg); \
int __sec = page_to_section(__pg); \
- (unsigned long)(__pg - __section_mem_map_addr(__nr_to_section(__sec))); \
+ (unsigned long)(ptr_diff(__pg, __section_mem_map_addr(__nr_to_section(__sec)))); \
})
#define __pfn_to_page(pfn) \
--
1.7.0.4
--
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