linux-kernel - Re: [PATCH] mm/mmap.c: optimization of do_mmap

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Date:	Mon, 8 Jun 2015 10:17:51 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Piotr Kwapulinski <kwapulinski.piotr@...il.com>
Cc:	akpm@...ux-foundation.org, kirill.shutemov@...ux.intel.com,
	riel@...hat.com, sasha.levin@...cle.com, dave@...olabs.net,
	koct9i@...il.com, pfeiner@...gle.com, dh.herrmann@...il.com,
	vishnu.ps@...sung.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/mmap.c: optimization of do_mmap_pgoff function

On Sat 06-06-15 11:54:32, Piotr Kwapulinski wrote:
> The simple check for zero length memory mapping may be performed
> earlier. It causes that in case of zero length memory mapping some
> unnecessary code is not executed at all. It does not make the code less
> readable and saves some CPU cycles.
> 
> Signed-off-by: Piotr Kwapulinski <kwapulinski.piotr@...il.com>

Acked-by: Michal Hocko <mhocko@...e.cz>

> ---
>  mm/mmap.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/mmap.c b/mm/mmap.c
> index bb50cac..aa632ad 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -1258,6 +1258,9 @@ unsigned long do_mmap_pgoff(struct file *file, unsigned long addr,
>  
>  	*populate = 0;
>  
> +	if (!len)
> +		return -EINVAL;
> +
>  	/*
>  	 * Does the application expect PROT_READ to imply PROT_EXEC?
>  	 *
> @@ -1268,9 +1271,6 @@ unsigned long do_mmap_pgoff(struct file *file, unsigned long addr,
>  		if (!(file && (file->f_path.mnt->mnt_flags & MNT_NOEXEC)))
>  			prot |= PROT_EXEC;
>  
> -	if (!len)
> -		return -EINVAL;
> -
>  	if (!(flags & MAP_FIXED))
>  		addr = round_hint_to_min(addr);
>  
> -- 
> 2.3.7
> 

-- 
Michal Hocko
SUSE Labs
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