linux-kernel - Re: [PATCH v2 03/35] lib/sbitmap; make __sbitmap_get_word() using find_and_set

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Message-ID: <20231204182228.7qzfgjyfmx7ubmx2@quack3>
Date:   Mon, 4 Dec 2023 19:22:28 +0100
From:   Jan Kara <jack@...e.cz>
To:     Yury Norov <yury.norov@...il.com>
Cc:     linux-kernel@...r.kernel.org, Jens Axboe <axboe@...nel.dk>,
        linux-block@...r.kernel.org, Jan Kara <jack@...e.cz>,
        Mirsad Todorovac <mirsad.todorovac@....unizg.hr>,
        Matthew Wilcox <willy@...radead.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Maxim Kuvyrkov <maxim.kuvyrkov@...aro.org>,
        Alexey Klimov <klimov.linux@...il.com>,
        Bart Van Assche <bvanassche@....org>,
        Sergey Shtylyov <s.shtylyov@....ru>
Subject: Re: [PATCH v2 03/35] lib/sbitmap; make __sbitmap_get_word() using
 find_and_set_bit()

On Sun 03-12-23 11:32:35, Yury Norov wrote:
> __sbitmap_get_word() opencodes either find_and_set_bit_wrap(), or
> find_and_set_next_bit() depending on hint and wrap parameters.
> 
> Switch it to use the atomic find_bit() API. While here, simplify
> sbitmap_find_bit_in_word(), which calls it.
> 
> Signed-off-by: Yury Norov <yury.norov@...il.com>

Looks good to me. Feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  lib/sbitmap.c | 46 ++++++++--------------------------------------
>  1 file changed, 8 insertions(+), 38 deletions(-)
> 
> diff --git a/lib/sbitmap.c b/lib/sbitmap.c
> index d0a5081dfd12..b21aebd07fd6 100644
> --- a/lib/sbitmap.c
> +++ b/lib/sbitmap.c
> @@ -133,38 +133,11 @@ void sbitmap_resize(struct sbitmap *sb, unsigned int depth)
>  }
>  EXPORT_SYMBOL_GPL(sbitmap_resize);
>  
> -static int __sbitmap_get_word(unsigned long *word, unsigned long depth,
> +static inline int __sbitmap_get_word(unsigned long *word, unsigned long depth,
>  			      unsigned int hint, bool wrap)
>  {
> -	int nr;
> -
> -	/* don't wrap if starting from 0 */
> -	wrap = wrap && hint;
> -
> -	while (1) {
> -		nr = find_next_zero_bit(word, depth, hint);
> -		if (unlikely(nr >= depth)) {
> -			/*
> -			 * We started with an offset, and we didn't reset the
> -			 * offset to 0 in a failure case, so start from 0 to
> -			 * exhaust the map.
> -			 */
> -			if (hint && wrap) {
> -				hint = 0;
> -				continue;
> -			}
> -			return -1;
> -		}
> -
> -		if (!test_and_set_bit_lock(nr, word))
> -			break;
> -
> -		hint = nr + 1;
> -		if (hint >= depth - 1)
> -			hint = 0;
> -	}
> -
> -	return nr;
> +	return wrap ? find_and_set_bit_wrap_lock(word, depth, hint) :
> +			find_and_set_next_bit_lock(word, depth, hint);
>  }
>  
>  static int sbitmap_find_bit_in_word(struct sbitmap_word *map,
> @@ -175,15 +148,12 @@ static int sbitmap_find_bit_in_word(struct sbitmap_word *map,
>  	int nr;
>  
>  	do {
> -		nr = __sbitmap_get_word(&map->word, depth,
> -					alloc_hint, wrap);
> -		if (nr != -1)
> -			break;
> -		if (!sbitmap_deferred_clear(map))
> -			break;
> -	} while (1);
> +		nr = __sbitmap_get_word(&map->word, depth, alloc_hint, wrap);
> +		if (nr < depth)
> +			return nr;
> +	} while (sbitmap_deferred_clear(map));
>  
> -	return nr;
> +	return -1;
>  }
>  
>  static int sbitmap_find_bit(struct sbitmap *sb,
> -- 
> 2.40.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR