Commit 2a98dc028f91 ("include/linux/bitmap.h: turn bitmap_set and
bitmap_clear into memset when possible", 2017-07-10) added an
optimization which effectively assumes that a contiguous set of
bits in a bitmap will be stored in a contiguous set of bytes of
the bitmap, in the case where the starting bit number and number of
bits are multiples of 8. This is true for a little-endian
representation, but not for a big-endian representation, because we
number the bits of a long from right to left for both little-endian
and big-endian representations.
The optimization can still be done for big-endian platforms, but
only if the starting bit number and number of bits are multiples
of BITS_PER_LONG. This adjusts the code to use 8 for little-endian
and BITS_PER_LONG for big-endian platforms.
Cc: sta...@vger.kernel.org # v4.13
Fixes: 2a98dc028f91 ("include/linux/bitmap.h: turn bitmap_set and bitmap_clear
into memset when possible")
Signed-off-by: Paul Mackerras <pau...@ozlabs.org>
---
This was found by inspection.
I'm pretty sure commit 2c6deb01525a is wrong as well on big-endian
machines.
include/linux/bitmap.h | 14 ++++++++++----
1 file changed, 10 insertions(+), 4 deletions(-)
diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
index 700cf5f..44e2eb4 100644
--- a/include/linux/bitmap.h
+++ b/include/linux/bitmap.h
@@ -174,8 +174,10 @@ extern unsigned int bitmap_to_u32array(u32 *buf,
unsigned int nbits);
#ifdef __BIG_ENDIAN
extern void bitmap_copy_le(unsigned long *dst, const unsigned long *src,
unsigned int nbits);
+#define BITMAP_MIN_UNIT BITS_PER_LONG /* have to access as longs */
#else
#define bitmap_copy_le bitmap_copy
+#define BITMAP_MIN_UNIT 8 /* can access as bytes if
desired */
#endif
extern unsigned int bitmap_ord_to_pos(const unsigned long *bitmap, unsigned
int ord, unsigned int nbits);
extern int bitmap_print_to_pagebuf(bool list, char *buf,
@@ -317,8 +319,10 @@ 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))
+ else if (__builtin_constant_p(start & (BITMAP_MIN_UNIT-1)) &&
+ IS_ALIGNED(start, BITMAP_MIN_UNIT) &&
+ __builtin_constant_p(nbits & (BITMAP_MIN_UNIT-1)) &&
+ IS_ALIGNED(nbits, BITMAP_MIN_UNIT))
memset((char *)map + start / 8, 0xff, nbits / 8);
else
__bitmap_set(map, start, nbits);
@@ -329,8 +333,10 @@ 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))
+ else if (__builtin_constant_p(start & (BITMAP_MIN_UNIT-1)) &&
+ IS_ALIGNED(start, BITMAP_MIN_UNIT) &&
+ __builtin_constant_p(nbits & (BITMAP_MIN_UNIT-1)) &&
+ IS_ALIGNED(nbits, BITMAP_MIN_UNIT))
memset((char *)map + start / 8, 0, nbits / 8);
else
__bitmap_clear(map, start, nbits);
--
2.7.4
