linux-kernel - Re: [PATCH] mm/sparse: return right away if sparsemap

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Message-ID: <ZqY81pf9dvl6mvg9@kernel.org>
Date: Sun, 28 Jul 2024 15:43:02 +0300
From: Mike Rapoport <rppt@...nel.org>
To: Leesoo Ahn <lsahn@...eel.net>
Cc: Leesoo Ahn <lsahn@...akecorp.com>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/sparse: return right away if sparsemap_buf is null

On Fri, Jul 26, 2024 at 04:10:23PM +0900, Leesoo Ahn wrote:
> sparse_buffer_fini(..) takes the following actions even though the value of
> sparsemap_buf is NULL,
> 1. calculate size of sparsemap buffer (which is meaningless).
> 2. set sparsemap_buf variable to NULL (although it is already NULL).
> 
> These steps are unnecessary if the variable, sparsemap_buf is NULL.
> 
> Refactor the function to return right away if the variable is NULL.
> Hence, it doesn't need to take further actions.

sparse_buffer_fini() is called a few times on init so saving a jump (if at
all) does not worth the churn.
 
> Signed-off-by: Leesoo Ahn <lsahn@...eel.net>
> ---
>  mm/sparse.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/sparse.c b/mm/sparse.c
> index e4b830091d13..091e4bc2f72c 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -469,9 +469,13 @@ static void __init sparse_buffer_init(unsigned long size, int nid)
>  
>  static void __init sparse_buffer_fini(void)
>  {
> -	unsigned long size = sparsemap_buf_end - sparsemap_buf;
> +	unsigned long size;
>  
> -	if (sparsemap_buf && size > 0)
> +	if (!sparsemap_buf)
> +		return;
> +
> +	size = sparsemap_buf_end - sparsemap_buf;
> +	if (size > 0)
>  		sparse_buffer_free(size);
>  	sparsemap_buf = NULL;
>  }
> -- 
> 2.34.1
> 
> 

-- 
Sincerely yours,
Mike.