linux-kernel - [PATCH 3/3] bitmap: Use memcmp optimisation in more situations

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Date:   Wed,  7 Jun 2017 07:29:24 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     linux-kernel@...r.kernel.org
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Matthew Wilcox <mawilcox@...rosoft.com>
Subject: [PATCH 3/3] bitmap: Use memcmp optimisation in more situations

From: Matthew Wilcox <mawilcox@...rosoft.com>

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.

Signed-off-by: Matthew Wilcox <mawilcox@...rosoft.com>
---
 include/linux/bitmap.h | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
index 0b3e4452b054..26244e0098f0 100644
--- a/include/linux/bitmap.h
+++ b/include/linux/bitmap.h
@@ -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);
 }
 
-- 
2.11.0