linux-kernel - Re: [PATCH] arm64: mm: use bitmap

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Message-ID: <20230516132427.GA30894@willie-the-truck>
Date:   Tue, 16 May 2023 14:24:28 +0100
From:   Will Deacon <will@...nel.org>
To:     ye.xingchen@....com.cn
Cc:     broonie@...nel.org, catalin.marinas@....com,
        kristina.martsenko@....com, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: mm: use bitmap_zero() API

On Sat, May 06, 2023 at 04:36:31PM +0800, ye.xingchen@....com.cn wrote:
> From: Ye Xingchen <ye.xingchen@....com.cn>
> 
> bitmap_zero() is faster than bitmap_clear(), so use bitmap_zero()
> instead of bitmap_clear().

Is it? Don't these both boil down to:

	memset(asid_map, 0, NUM_USER_ASIDS / 8)

?

Will

> ---
>  arch/arm64/mm/context.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/mm/context.c b/arch/arm64/mm/context.c
> index e1e0dca01839..ed0bf7f8e8ce 100644
> --- a/arch/arm64/mm/context.c
> +++ b/arch/arm64/mm/context.c
> @@ -95,7 +95,7 @@ static void set_reserved_asid_bits(void)
>  	else if (arm64_kernel_unmapped_at_el0())
>  		set_kpti_asid_bits(asid_map);
>  	else
> -		bitmap_clear(asid_map, 0, NUM_USER_ASIDS);
> +		bitmap_zero(asid_map, NUM_USER_ASIDS);
>  }
> 
>  #define asid_gen_match(asid) \
> -- 
> 2.25.1