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Date: Thu, 7 Jul 2011 15:12:52 -0500 (CDT)
From: Christoph Lameter <cl@...ux.com>
To: Pekka Enberg <penberg@...nel.org>
cc: David Miller <davem@...emloft.net>, marcin.slusarz@...il.com,
mpm@...enic.com, linux-kernel@...r.kernel.org, rientjes@...gle.com,
linux-mm@...ck.org
Subject: Re: [PATCH] slub: reduce overhead of slub_debug
On Thu, 7 Jul 2011, Pekka Enberg wrote:
> I applied the patch. I think a follow up patch that moves the function
> to lib/string.c with proper generic name would be in order. Thanks!
Well this is really straightforward. Hasnt seen much testing yet and
needs refinement but it would be like this:
---
arch/x86/include/asm/string_32.h | 2 ++
arch/x86/lib/string_32.c | 17 +++++++++++++++++
include/linux/string.h | 3 +++
lib/string.c | 25 +++++++++++++++++++++++++
mm/slub.c | 13 ++++++-------
5 files changed, 53 insertions(+), 7 deletions(-)
Index: linux-2.6/arch/x86/lib/string_32.c
===================================================================
--- linux-2.6.orig/arch/x86/lib/string_32.c 2011-07-07 15:03:46.000000000 -0500
+++ linux-2.6/arch/x86/lib/string_32.c 2011-07-07 15:03:56.000000000 -0500
@@ -214,6 +214,23 @@ void *memscan(void *addr, int c, size_t
EXPORT_SYMBOL(memscan);
#endif
+#ifdef __HAVE_ARCH_INV_MEMSCAN
+void *inv_memscan(void *addr, int c, size_t size)
+{
+ if (!size)
+ return addr;
+ asm volatile("repz; scasb\n\t"
+ "jz 1f\n\t"
+ "dec %%edi\n"
+ "1:"
+ : "=D" (addr), "=c" (size)
+ : "0" (addr), "1" (size), "a" (c)
+ : "memory");
+ return addr;
+}
+EXPORT_SYMBOL(memscan);
+#endif
+
#ifdef __HAVE_ARCH_STRNLEN
size_t strnlen(const char *s, size_t count)
{
Index: linux-2.6/include/linux/string.h
===================================================================
--- linux-2.6.orig/include/linux/string.h 2011-07-07 15:03:46.000000000 -0500
+++ linux-2.6/include/linux/string.h 2011-07-07 15:03:56.000000000 -0500
@@ -108,6 +108,9 @@ extern void * memmove(void *,const void
#ifndef __HAVE_ARCH_MEMSCAN
extern void * memscan(void *,int,__kernel_size_t);
#endif
+#ifndef __HAVE_ARCH_INV_MEMSCAN
+extern void * inv_memscan(void *,int,__kernel_size_t);
+#endif
#ifndef __HAVE_ARCH_MEMCMP
extern int memcmp(const void *,const void *,__kernel_size_t);
#endif
Index: linux-2.6/lib/string.c
===================================================================
--- linux-2.6.orig/lib/string.c 2011-07-07 15:03:46.000000000 -0500
+++ linux-2.6/lib/string.c 2011-07-07 15:03:56.000000000 -0500
@@ -684,6 +684,31 @@ void *memscan(void *addr, int c, size_t
EXPORT_SYMBOL(memscan);
#endif
+#ifndef __HAVE_ARCH_INV_MEMSCAN
+/**
+ * memscan - Skip characters in an area of memory.
+ * @addr: The memory area
+ * @c: The byte to skip
+ * @size: The size of the area.
+ *
+ * returns the address of the first mismatch of @c, or 1 byte past
+ * the area if @c matches to the end
+ */
+void *inv_memscan(void *addr, int c, size_t size)
+{
+ unsigned char *p = addr;
+
+ while (size) {
+ if (*p != c)
+ return (void *)p;
+ p++;
+ size--;
+ }
+ return (void *)p;
+}
+EXPORT_SYMBOL(inv_memscan);
+#endif
+
#ifndef __HAVE_ARCH_STRSTR
/**
* strstr - Find the first substring in a %NUL terminated string
Index: linux-2.6/arch/x86/include/asm/string_32.h
===================================================================
--- linux-2.6.orig/arch/x86/include/asm/string_32.h 2011-07-07 15:05:44.000000000 -0500
+++ linux-2.6/arch/x86/include/asm/string_32.h 2011-07-07 15:06:16.000000000 -0500
@@ -336,6 +336,8 @@ void *__constant_c_and_count_memset(void
*/
#define __HAVE_ARCH_MEMSCAN
extern void *memscan(void *addr, int c, size_t size);
+#define __HAVE_ARCH_INV_MEMSCAN
+extern void *inv_memscan(void *addr, int c, size_t size);
#endif /* __KERNEL__ */
Index: linux-2.6/mm/slub.c
===================================================================
--- linux-2.6.orig/mm/slub.c 2011-07-07 15:04:11.000000000 -0500
+++ linux-2.6/mm/slub.c 2011-07-07 15:10:21.000000000 -0500
@@ -559,13 +559,12 @@ static void init_object(struct kmem_cach
static u8 *check_bytes(u8 *start, unsigned int value, unsigned int bytes)
{
- while (bytes) {
- if (*start != (u8)value)
- return start;
- start++;
- bytes--;
- }
- return NULL;
+ u8 *p = inv_memscan(start, value, bytes);
+
+ if (p == start + bytes)
+ return NULL;
+
+ return p;
}
static void restore_bytes(struct kmem_cache *s, char *message, u8 data,
--
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