From patchwork Wed Sep  1 10:36:33 2010
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Date: Wed, 01 Sep 2010 18:36:33 +0800
From: Miao Xie <miaox@cn.fujitsu.com>
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To: Ingo Molnar <mingo@redhat.com>, Andrew Morton <akpm@linux-foundation.org>,
	"Theodore Ts'o" <tytso@mit.edu>, Chris Mason <chris.mason@oracle.com>,
	Andreas Dilger <adilger.kernel@dilger.ca>,
	Linux Kernel <linux-kernel@vger.kernel.org>,
	Linux Btrfs <linux-btrfs@vger.kernel.org>,
	Linux Ext4 <linux-ext4@vger.kernel.org>
Subject: [PATCH 3/3] x86_64/lib: improve the performance of memmove
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diff --git a/arch/x86/lib/memmove_64.c b/arch/x86/lib/memmove_64.c
index 0a33909..3640232 100644
--- a/arch/x86/lib/memmove_64.c
+++ b/arch/x86/lib/memmove_64.c
@@ -4,17 +4,17 @@
 #define _STRING_C
 #include <linux/string.h>
 #include <linux/module.h>
+#include <linux/memcopy.h>
 
 #undef memmove
 void *memmove(void *dest, const void *src, size_t count)
 {
-	if (dest < src) {
+	if (dest - src >= count) {	/* *Unsigned* compare! */
 		return memcpy(dest, src, count);
 	} else {
-		char *p = dest + count;
-		const char *s = src + count;
-		while (count--)
-			*--p = *--s;
+		unsigned long dstp = (unsigned long)dest;
+		unsigned long srcp = (unsigned long)src;
+		mem_copy_bwd(dstp, srcp, count);
 	}
 	return dest;
 }