include/linux/bitmap.h: turn bitmap_set and bitmap_clear into memset when possible

Several callers have constant 'start' and an 'nbits' that is a multiple
of 8, so we can turn them into calls to memset.  We don't need the
entirety of 'start' and 'nbits' to be constant, we just need to know
whether they're divisible by 8.

Link: http://lkml.kernel.org/r/20170628153221.11322-4-willy@infradead.org
Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Acked-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
index 4e0f0c8167af753898b814249677b71c440eeb2e..c04c9d155e59c4df3a8ce40d9126744ff50fb403 100644 (file)
--- a/include/linux/bitmap.h
+++ b/include/linux/bitmap.h
@@ -319,6 +319,9 @@ static __always_inline void bitmap_set(unsigned long *map, unsigned int start,
 {
        if (__builtin_constant_p(nbits) && nbits == 1)
                __set_bit(start, map);
+       else if (__builtin_constant_p(start & 7) && IS_ALIGNED(start, 8) &&
+                __builtin_constant_p(nbits & 7) && IS_ALIGNED(nbits, 8))
+               memset((char *)map + start / 8, 0xff, nbits / 8);
        else
                __bitmap_set(map, start, nbits);
 }
@@ -328,6 +331,9 @@ static __always_inline void bitmap_clear(unsigned long *map, unsigned int start,
 {
        if (__builtin_constant_p(nbits) && nbits == 1)
                __clear_bit(start, map);
+       else if (__builtin_constant_p(start & 7) && IS_ALIGNED(start, 8) &&
+                __builtin_constant_p(nbits & 7) && IS_ALIGNED(nbits, 8))
+               memset((char *)map + start / 8, 0, nbits / 8);
        else
                __bitmap_clear(map, start, nbits);
 }