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

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Date:   Mon, 4 Dec 2023 11:40:59 -0700
From:   Jens Axboe <axboe@...nel.dk>
To:     Yury Norov <yury.norov@...il.com>, linux-kernel@...r.kernel.org,
        linux-block@...r.kernel.org
Cc:     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 12/3/23 12:32 PM, Yury Norov wrote:
> 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);
>  }

Please make this:

	if (wrap)
		return find_and_set_bit_wrap_lock(word, depth, hint) :
	return find_and_set_next_bit_lock(word, depth, hint);

so this is a lot more readable.

-- 
Jens Axboe