From: Yury Norov <yury.norov@xxxxxxxxx> Subject: lib: extend the scope of small_const_nbits() macro find_bit would also benefit from small_const_nbits() optimizations. The detailed comment is provided by Rasmus Villemoes. Link: https://lkml.kernel.org/r/20210401003153.97325-6-yury.norov@xxxxxxxxx Suggested-by: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx> Signed-off-by: Yury Norov <yury.norov@xxxxxxxxx> Acked-by: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx> Acked-by: Andy Shevchenko <andy.shevchenko@xxxxxxxxx> Cc: Alexey Klimov <aklimov@xxxxxxxxxx> Cc: Arnd Bergmann <arnd@xxxxxxxx> Cc: David Sterba <dsterba@xxxxxxxx> Cc: Dennis Zhou <dennis@xxxxxxxxxx> Cc: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> Cc: Jianpeng Ma <jianpeng.ma@xxxxxxxxx> Cc: Joe Perches <joe@xxxxxxxxxxx> Cc: John Paul Adrian Glaubitz <glaubitz@xxxxxxxxxxxxxxxxxxx> Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> Cc: Rich Felker <dalias@xxxxxxxx> Cc: Stefano Brivio <sbrivio@xxxxxxxxxx> Cc: Wei Yang <richard.weiyang@xxxxxxxxxxxxxxxxx> Cc: Wolfram Sang <wsa+renesas@xxxxxxxxxxxxxxxxxxxx> Cc: Yoshinori Sato <ysato@xxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- include/asm-generic/bitsperlong.h | 12 ++++++++++++ include/linux/bitmap.h | 8 -------- 2 files changed, 12 insertions(+), 8 deletions(-) --- a/include/asm-generic/bitsperlong.h~lib-extend-the-scope-of-small_const_nbits-macro +++ a/include/asm-generic/bitsperlong.h @@ -23,4 +23,16 @@ #define BITS_PER_LONG_LONG 64 #endif +/* + * small_const_nbits(n) is true precisely when it is known at compile-time + * that BITMAP_SIZE(n) is 1, i.e. 1 <= n <= BITS_PER_LONG. This allows + * various bit/bitmap APIs to provide a fast inline implementation. Bitmaps + * of size 0 are very rare, and a compile-time-known-size 0 is most likely + * a sign of error. They will be handled correctly by the bit/bitmap APIs, + * but using the out-of-line functions, so that the inline implementations + * can unconditionally dereference the pointer(s). + */ +#define small_const_nbits(nbits) \ + (__builtin_constant_p(nbits) && (nbits) <= BITS_PER_LONG && (nbits) > 0) + #endif /* __ASM_GENERIC_BITS_PER_LONG */ --- a/include/linux/bitmap.h~lib-extend-the-scope-of-small_const_nbits-macro +++ a/include/linux/bitmap.h @@ -223,14 +223,6 @@ extern int bitmap_print_to_pagebuf(bool #define BITMAP_FIRST_WORD_MASK(start) (~0UL << ((start) & (BITS_PER_LONG - 1))) #define BITMAP_LAST_WORD_MASK(nbits) (~0UL >> (-(nbits) & (BITS_PER_LONG - 1))) -/* - * The static inlines below do not handle constant nbits==0 correctly, - * so make such users (should any ever turn up) call the out-of-line - * versions. - */ -#define small_const_nbits(nbits) \ - (__builtin_constant_p(nbits) && (nbits) <= BITS_PER_LONG && (nbits) > 0) - static inline void bitmap_zero(unsigned long *dst, unsigned int nbits) { unsigned int len = BITS_TO_LONGS(nbits) * sizeof(unsigned long); _
