Re: [PATCH v2] mm: huge_memory: convert split_huge_pages_all() to use a folio

[Kefeng Wang <wangkefeng.wang@huawei.com>]

On 2022/12/31 5:45, Andrew Morton wrote:
> On Fri, 30 Dec 2022 17:30:20 +0800 Kefeng Wang <wangkefeng.wang@huawei.com> wrote:
> 
>> Straightforwardly convert split_huge_pages_all() to use a folio.
>>
>> ...
>>
>> --- a/mm/huge_memory.c
>> +++ b/mm/huge_memory.c
>> @@ -2932,6 +2932,7 @@ static void split_huge_pages_all(void)
>>   {
>>   	struct zone *zone;
>>   	struct page *page;
>> +	struct folio *folio;
>>   	unsigned long pfn, max_zone_pfn;
>>   	unsigned long total = 0, split = 0;
>>   
>> @@ -2944,24 +2945,32 @@ static void split_huge_pages_all(void)
>>   			int nr_pages;
>>   
>>   			page = pfn_to_online_page(pfn);
>> -			if (!page || !get_page_unless_zero(page))
>> +			if (!page || PageTail(page))
>> +				continue;
>> +			folio = page_folio(page);
>> +			if (!folio_try_get(folio))
>>   				continue;
>>   
>> -			if (zone != page_zone(page))
>> +			if (unlikely(page_folio(page) != folio))
>> +				goto next;
>> +
>> +			if (zone != folio_zone(folio))
>>   				goto next;
> 
> I'm still not understanding the above hunk.  Why is the
> "page_folio(page) != folio" check added?  Should it be commented?

There is a comment in try_get_folio(), is it enough?