Commit 2c6deb01 authored Jul 10, 2017 by Matthew Wilcox Committed by Linus Torvalds Jul 10, 2017

bitmap: use memcmp optimisation in more situations

Commit 7dd96816 ("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>

parent 2a98dc02

arch/arm/boot/compressed/decompress.c

+1 −0

Original line number	Diff line number	Diff line
		@@ -33,6 +33,7 @@ extern void error(char *);
		/* Not needed, but used in some headers pulled in by decompressors */
		extern char * strstr(const char * s1, const char *s2);
		extern size_t strlen(const char *s);
		extern int memcmp(const void cs, const void ct, size_t count);

		#ifdef CONFIG_KERNEL_GZIP
		#include "../../../../lib/decompress_inflate.c"

include/linux/bitmap.h

+1 −3

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

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