linux-kernel - Re: [PATCH RESEND] sh: sq: Use the bitmap API when applicable

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Date:   Tue, 18 Apr 2023 08:36:40 +0200
From:   John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>
To:     Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>
Cc:     linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org,
        linux-sh@...r.kernel.org, Geert Uytterhoeven <geert@...ux-m68k.org>
Subject: Re: [PATCH RESEND] sh: sq: Use the bitmap API when applicable

Hi Christophe!

Thanks for your patch. The changes look good to me. However, I have
one question, see below.

On Sun, 2023-04-16 at 21:05 +0200, Christophe JAILLET wrote:
> Using the bitmap API is less verbose than hand writing them.
> It also improves the semantic.
> 
> Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
> ---
> This is a resend of [1].
> 
> Now cross-compile tested with CONFIG_CPU_SUBTYPE_SH7770=y
> 
> [1]: https://lore.kernel.org/all/521788e22ad8f7a5058c154f068b061525321841.1656142814.git.christophe.jaillet@wanadoo.fr/
> ---
>  arch/sh/kernel/cpu/sh4/sq.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/sh/kernel/cpu/sh4/sq.c b/arch/sh/kernel/cpu/sh4/sq.c
> index 27f2e3da5aa2..d289e99dc118 100644
> --- a/arch/sh/kernel/cpu/sh4/sq.c
> +++ b/arch/sh/kernel/cpu/sh4/sq.c
> @@ -372,7 +372,6 @@ static struct subsys_interface sq_interface = {
>  static int __init sq_api_init(void)
>  {
>  	unsigned int nr_pages = 0x04000000 >> PAGE_SHIFT;
> -	unsigned int size = (nr_pages + (BITS_PER_LONG - 1)) / BITS_PER_LONG;
>  	int ret = -ENOMEM;
>  
>  	printk(KERN_NOTICE "sq: Registering store queue API.\n");
> @@ -382,7 +381,7 @@ static int __init sq_api_init(void)
>  	if (unlikely(!sq_cache))
>  		return ret;
>  
> -	sq_bitmap = kzalloc(size, GFP_KERNEL);
> +	sq_bitmap = bitmap_zalloc(nr_pages, GFP_KERNEL);
>  	if (unlikely(!sq_bitmap))
>  		goto out;
> 

I have look through other patches where k{z,c,m}alloc() were replaced with
bitmap_zalloc() and I noticed that in the other cases such as [1], kcalloc()
was used instead of kzalloc() in our cases with the element size set to
sizeof(long) while kzalloc() is using an element size equal to a byte.

Wouldn't that mean that the current code in sq is allocating a buffer that is
too small by a factor of 1/sizeof(long) or am I missing something?

@Geert: Do you have any idea?

> @@ -393,7 +392,7 @@ static int __init sq_api_init(void)
>  	return 0;
>  
>  out:
> -	kfree(sq_bitmap);
> +	bitmap_free(sq_bitmap);
>  	kmem_cache_destroy(sq_cache);
>  
>  	return ret;
> @@ -402,7 +401,7 @@ static int __init sq_api_init(void)
>  static void __exit sq_api_exit(void)
>  {
>  	subsys_interface_unregister(&sq_interface);
> -	kfree(sq_bitmap);
> +	bitmap_free(sq_bitmap);
>  	kmem_cache_destroy(sq_cache);
>  }
>  

Adrian

> [1] https://lkml.org/lkml/2021/11/28/155

-- 
 .''`.  John Paul Adrian Glaubitz
: :' :  Debian Developer
`. `'   Physicist
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