linux-kernel - Re: [PATCH 1/2] drivers/base/memory: Simplify add_boot_memory

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Message-ID: <a33fcf3f-0694-427a-b10c-e99a50d36e02@redhat.com>
Date: Sat, 15 Feb 2025 09:45:05 +1000
From: Gavin Shan <gshan@...hat.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org, david@...hat.com,
 osalvador@...e.de, gregkh@...uxfoundation.org, rafael@...nel.org,
 dakr@...nel.org
Subject: Re: [PATCH 1/2] drivers/base/memory: Simplify add_boot_memory_block()

On 2/15/25 8:57 AM, Andrew Morton wrote:
> On Fri, 14 Feb 2025 16:35:03 +1000 Gavin Shan <gshan@...hat.com> wrote:
> 
>> It's unnecessary to keep the variable @section_count in the function
>> because the device for the specific memory block will be added if
>> any of its memory section is present. The variable @section_count
>> records the number of present memory sections in the specific memory
>> block, which isn't needed.
>>
>> Simplify the function by dropping the variable @section_count. No
>> functional change intended.
>>
>> ...
>>
>>   static int __init add_boot_memory_block(unsigned long base_section_nr)
>>   {
>> -	int section_count = 0;
>>   	unsigned long nr;
>>   
>>   	for (nr = base_section_nr; nr < base_section_nr + sections_per_block;
> 
> mm/sparse.c has a for_each_present_section_nr() - is that usable here?
> 

It should be fine to use it. I will add one preparatory patch to expose
for_each_present_section_nr(). With it, the nested if statements can also
be avoided, Something like below.

         for_each_present_section_nr(base_section_nr - 1, nr) {
		if (nr >= base_section_nr + sections_per_block)
			break;

		return add_memory_block(memory_block_id(nr), MEM_ONLINE, NULL, NULL);
         }

	return 0;

>> -	     nr++)
>> -		if (present_section_nr(nr))
>> -			section_count++;
>> +	     nr++) {
>> +		if (present_section_nr(nr)) {
>> +			return add_memory_block(memory_block_id(base_section_nr),
>> +						MEM_ONLINE, NULL, NULL);
>> +		}
>> +	}
>>

Thanks,
Gavin