linux-kernel - Re: [RFC PATCH] mm/zsmalloc: remove unnecessary check

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Date:	Fri, 21 Nov 2014 12:54:42 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Mahendran Ganesh <opensource.ganesh@...il.com>
Cc:	ngupta@...are.org, iamjoonsoo.kim@....com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] mm/zsmalloc: remove unnecessary check

On Thu, Nov 20, 2014 at 09:21:56PM +0800, Mahendran Ganesh wrote:
> ZS_SIZE_CLASSES is calc by:
>   ((ZS_MAX_ALLOC_SIZE - ZS_MIN_ALLOC_SIZE) / ZS_SIZE_CLASS_DELTA + 1)
> 
> So when i is in [0, ZS_SIZE_CLASSES - 1), the size:
>   size = ZS_MIN_ALLOC_SIZE + i * ZS_SIZE_CLASS_DELTA
> will not be greater than ZS_MAX_ALLOC_SIZE
> 
> This patch removes the unnecessary check.

It depends on ZS_MIN_ALLOC_SIZE.
For example, we would change min to 8 but MAX is still 4096.
ZS_SIZE_CLASSES is (4096 - 8) / 16 + 1 = 256 so 8 + 255 * 16 = 4088,
which exceeds the max.

> 
> Signed-off-by: Mahendran Ganesh <opensource.ganesh@...il.com>
> ---
>  mm/zsmalloc.c |    2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index b3b57ef..f2279e2 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -973,8 +973,6 @@ struct zs_pool *zs_create_pool(gfp_t flags)
>  		struct size_class *prev_class;
>  
>  		size = ZS_MIN_ALLOC_SIZE + i * ZS_SIZE_CLASS_DELTA;
> -		if (size > ZS_MAX_ALLOC_SIZE)
> -			size = ZS_MAX_ALLOC_SIZE;
>  		pages_per_zspage = get_pages_per_zspage(size);
>  
>  		/*
> -- 
> 1.7.9.5
> 
> --
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-- 
Kind regards,
Minchan Kim
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