linux-kernel - Re: [PATCH] include/linux/gfp.h: use unsigned int in gfp

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Date:   Thu, 3 May 2018 09:43:27 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Huaisheng Ye <yehs1@...ovo.com>
Cc:     akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, vbabka@...e.cz,
        mgorman@...hsingularity.net, alexander.levin@...izon.com,
        colyli@...e.de, chengnt@...ovo.com
Subject: Re: [PATCH] include/linux/gfp.h: use unsigned int in gfp_zone

On Thu 03-05-18 11:44:58, Huaisheng Ye wrote:
> Suggest using unsigned int instead of int for bit within gfp_zone.
> 
> The value of bit comes from flags, which's type is gfp_t. And it
> indicates the number of bits in the right shift for GFP_ZONE_TABLE.
> 
> Signed-off-by: Huaisheng Ye <yehs1@...ovo.com>

The patch looks OK but it misses the most important piece of
information. Why this is worth changing. Does it lead to a better code?
Silence a warning or...

> ---
>  include/linux/gfp.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/gfp.h b/include/linux/gfp.h
> index 1a4582b..21551fc 100644
> --- a/include/linux/gfp.h
> +++ b/include/linux/gfp.h
> @@ -401,7 +401,7 @@ static inline bool gfpflags_allow_blocking(const gfp_t gfp_flags)
>  static inline enum zone_type gfp_zone(gfp_t flags)
>  {
>  	enum zone_type z;
> -	int bit = (__force int) (flags & GFP_ZONEMASK);
> +	unsigned int bit = (__force unsigned int) (flags & GFP_ZONEMASK);
>  
>  	z = (GFP_ZONE_TABLE >> (bit * GFP_ZONES_SHIFT)) &
>  					 ((1 << GFP_ZONES_SHIFT) - 1);
> -- 
> 1.8.3.1
> 

-- 
Michal Hocko
SUSE Labs