linux-kernel - Re: [PATCH] mm/slab_common: use helper function is_power_of

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Message-ID: <8f307e8a-5f97-cf5d-0a77-1c79b05abd60@suse.cz>
Date:   Thu, 17 Feb 2022 10:23:11 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Miaohe Lin <linmiaohe@...wei.com>, akpm@...ux-foundation.org,
        cl@...ux.com, penberg@...nel.org, rientjes@...gle.com,
        iamjoonsoo.kim@....com
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/slab_common: use helper function is_power_of_2()

On 2/17/22 10:16, Miaohe Lin wrote:
> Use helper function is_power_of_2() to check if KMALLOC_MIN_SIZE is power
> of two. Minor readability improvement.
> 
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>

We can try, but in case some compiler will no longer able to perform the
check at build-time (although is_power_of_2() looks sufficiently trivial
too), we'll have to revert it.

> ---
>  mm/slab_common.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 23f2ab0713b7..6ee64d6208b3 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -807,7 +807,7 @@ void __init setup_kmalloc_cache_index_table(void)
>  	unsigned int i;
>  
>  	BUILD_BUG_ON(KMALLOC_MIN_SIZE > 256 ||
> -		(KMALLOC_MIN_SIZE & (KMALLOC_MIN_SIZE - 1)));
> +		!is_power_of_2(KMALLOC_MIN_SIZE));
>  
>  	for (i = 8; i < KMALLOC_MIN_SIZE; i += 8) {
>  		unsigned int elem = size_index_elem(i);