The patch titled
Subject: lib/string: optimized memmove
has been added to the -mm tree. Its filename is
lib-string-optimized-memmove.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/lib-string-optimized-memmove.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/lib-string-optimized-memmove.patch
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*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next and is updated
there every 3-4 working days
------------------------------------------------------
From: Matteo Croce <mcroce@xxxxxxxxxxxxx>
Subject: lib/string: optimized memmove
When the destination buffer is before the source one, or when the buffers
doesn't overlap, it's safe to use memcpy() instead, which is optimized to
use a bigger data size possible.
This "optimization" only covers a common case. In future, proper code
which does the same thing as memcpy() does but backwards can be done.
Link: https://lkml.kernel.org/r/20210702123153.14093-3-mcroce@xxxxxxxxxxxxxxxxxxx
Signed-off-by: Matteo Croce <mcroce@xxxxxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Cc: David Laight <David.Laight@xxxxxxxxxx>
Cc: Drew Fustini <drew@xxxxxxxxxxxxxxx>
Cc: Emil Renner Berthing <kernel@xxxxxxxx>
Cc: Guo Ren <guoren@xxxxxxxxxx>
Cc: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Cc: Nick Kossifidis <mick@xxxxxxxxxxxx>
Cc: Palmer Dabbelt <palmer@xxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
lib/string.c | 18 ++++++------------
1 file changed, 6 insertions(+), 12 deletions(-)
--- a/lib/string.c~lib-string-optimized-memmove
+++ a/lib/string.c
@@ -975,19 +975,13 @@ EXPORT_SYMBOL(memcpy);
*/
void *memmove(void *dest, const void *src, size_t count)
{
- char *tmp;
- const char *s;
+ if (dest < src || src + count <= dest)
+ return memcpy(dest, src, count);
+
+ if (dest > src) {
+ const char *s = src + count;
+ char *tmp = dest + count;
- if (dest <= src) {
- tmp = dest;
- s = src;
- while (count--)
- *tmp++ = *s++;
- } else {
- tmp = dest;
- tmp += count;
- s = src;
- s += count;
while (count--)
*--tmp = *--s;
}
_
Patches currently in -mm which might be from mcroce@xxxxxxxxxxxxx are
revert-mm-page_alloc-make-should_fail_alloc_page-static.patch
lib-string-optimized-memcpy.patch
lib-string-optimized-memmove.patch
lib-string-optimized-memset.patch
