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bitmap: use memcmp optimisation in more situations

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Commit 7dd968163f ("bitmap: bitmap_equal memcmp optimization") was
rather more restrictive than necessary; we can use memcmp() to implement
bitmap_equal() as long as the number of bits can be proved to be a
multiple of 8.  And architectures other than s390 may be able to make
good use of this optimisation.

[arnd@arndb.de: fix build: add a memcmp() declaration]
  Link: http://lkml.kernel.org/r/20170630153908.3439707-1-arnd@arndb.de
Link: http://lkml.kernel.org/r/20170628153221.11322-5-willy@infradead.org
Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Matthew Wilcox 2017-07-10 15:51:35 -07:00 committed by Linus Torvalds
parent 2a98dc028f
commit 2c6deb0152
2 changed files with 2 additions and 3 deletions
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1
arch/arm/boot/compressed/decompress.c
View file

@ -33,6 +33,7 @@ extern void error(char *);
/* Not needed, but used in some headers pulled in by decompressors */ /* Not needed, but used in some headers pulled in by decompressors */
extern char * strstr(const char * s1, const char *s2); extern char * strstr(const char * s1, const char *s2);
extern size_t strlen(const char *s); extern size_t strlen(const char *s);
extern int memcmp(const void *cs, const void *ct, size_t count);
#ifdef CONFIG_KERNEL_GZIP #ifdef CONFIG_KERNEL_GZIP
#include "../../../../lib/decompress_inflate.c" #include "../../../../lib/decompress_inflate.c"

4
include/linux/bitmap.h
View file

@ -266,10 +266,8 @@ static inline int bitmap_equal(const unsigned long *src1,
{ {
if (small_const_nbits(nbits)) if (small_const_nbits(nbits))
return !((*src1 ^ *src2) & BITMAP_LAST_WORD_MASK(nbits)); return !((*src1 ^ *src2) & BITMAP_LAST_WORD_MASK(nbits));
#ifdef CONFIG_S390 if (__builtin_constant_p(nbits & 7) && IS_ALIGNED(nbits, 8))
if (__builtin_constant_p(nbits) && (nbits % BITS_PER_LONG) == 0)
return !memcmp(src1, src2, nbits / 8); return !memcmp(src1, src2, nbits / 8);
#endif
return __bitmap_equal(src1, src2, nbits); return __bitmap_equal(src1, src2, nbits);
} }