linux-kernel - Re: [PATCH v2 0/5] lib/find: add find_nth

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Date:   Thu, 21 Jul 2022 14:14:58 -0700
From:   Yury Norov <yury.norov@...il.com>
To:     linux-kernel@...r.kernel.org,
        Alexander Lobakin <alexandr.lobakin@...el.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Arnd Bergmann <arnd@...db.de>, David Gow <davidgow@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Isabella Basso <isabbasso@...eup.net>,
        Kees Cook <keescook@...omium.org>,
        Keith Busch <kbusch@...nel.org>,
        Kumar Kartikeya Dwivedi <memxor@...il.com>,
        Marco Elver <elver@...gle.com>,
        Mark Rutland <mark.rutland@....com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Steven Rostedt <rostedt@...dmis.org>,
        Toke Høiland-Jørgensen <toke@...hat.com>
Subject: Re: [PATCH v2 0/5] lib/find: add find_nth_bit()

If no other comments, except that fns() name, moving it in -next.

On Sun, Jul 10, 2022 at 09:47:06PM -0700, Yury Norov wrote:
> Kernel lacks for a function that searches for Nth bit in a bitmap.
> Usually people do it like this:
>         for_each_set_bit(bit, mask, size)
>                 if (--n == 0)
>                         return bit;
> 
> Which is not so elegant, and very slow.
> 
> This series adds fast routines for this task, and applies them where
> appropriate.
> 
> While here, move thin wrappers around find_bit() in nodemask.c to a
> corresponding header, and because nodemask.c is empty after that,
> remove it.
> 
> v1: https://lore.kernel.org/lkml/20220706182300.70862-4-yury.norov@gmail.com/T/
> v2: - count Nth bit from 0 (was 1);
>     - use 'invert' trick in _find_nth_bit(), as in _find_next_bit();
>     - cleanup comments;
>     - fns() is kept inline - looking at __ffs() generic implementation,
>       I decided to keep it untouched.
> 
> Yury Norov (5):
>   lib: add find_nth(,and,andnot)_bit()
>   lib/bitmap: add tests for find_nth_bit()
>   lib/bitmap: remove bitmap_ord_to_pos
>   cpumask: add cpumask_nth_{,and,andnot}
>   lib/nodemask: inline next_node_in() and node_random()
> 
>  MAINTAINERS              |  1 -
>  include/linux/bitmap.h   |  1 -
>  include/linux/bitops.h   | 19 +++++++++
>  include/linux/cpumask.h  | 44 +++++++++++++++++++++
>  include/linux/find.h     | 83 ++++++++++++++++++++++++++++++++++++++++
>  include/linux/nodemask.h | 27 ++++++++++---
>  lib/Makefile             |  2 +-
>  lib/bitmap.c             | 36 ++---------------
>  lib/cpumask.c            | 26 ++++++-------
>  lib/find_bit.c           | 20 ++++++++++
>  lib/find_bit_benchmark.c | 17 ++++++++
>  lib/nodemask.c           | 31 ---------------
>  lib/test_bitmap.c        | 36 ++++++++++++++++-
>  13 files changed, 254 insertions(+), 89 deletions(-)
>  delete mode 100644 lib/nodemask.c
> 
> -- 
> 2.34.1