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

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Message-ID: <f71502d2-d216-4377-965f-21583dd7dc31@arm.com>
Date: Mon, 29 Jul 2024 12:27:36 +0530
From: Anshuman Khandual <anshuman.khandual@....com>
To: Mike Rapoport <rppt@...nel.org>, 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 7/28/24 18:13, Mike Rapoport wrote:
> 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.

Agreed, this is not worth the churn given there could be just a single
call instance for sparse_buffer_fini(), either in normal or error path
in sparse_init_nid().

>  
>> 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
>>
>>
>