The patch titled
Subject: include/linux/bitmap.h: turn bitmap_set and bitmap_clear into memset when possible
has been added to the -mm tree. Its filename is
turn-bitmap_set-and-bitmap_clear-into-memset-when-possible.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/turn-bitmap_set-and-bitmap_clear-into-memset-when-possible.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/turn-bitmap_set-and-bitmap_clear-into-memset-when-possible.patch
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------------------------------------------------------
From: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
Subject: 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@xxxxxxxxxxxxx
Signed-off-by: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
Acked-by: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
Cc: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/bitmap.h | 6 ++++++
1 file changed, 6 insertions(+)
diff -puN include/linux/bitmap.h~turn-bitmap_set-and-bitmap_clear-into-memset-when-possible include/linux/bitmap.h
--- a/include/linux/bitmap.h~turn-bitmap_set-and-bitmap_clear-into-memset-when-possible
+++ a/include/linux/bitmap.h
@@ -319,6 +319,9 @@ static __always_inline void bitmap_set(u
{
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
{
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);
}
_
Patches currently in -mm which might be from mawilcox@xxxxxxxxxxxxx are
test_bitmap-add-optimisation-tests.patch
bitmap-optimise-bitmap_set-and-bitmap_clear-of-a-single-bit.patch
turn-bitmap_set-and-bitmap_clear-into-memset-when-possible.patch
bitmap-use-memcmp-optimisation-in-more-situations.patch
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