linux-kernel - Re: [PATCH v2] mm: huge_memory: convert split_huge_pages

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Date:   Tue, 3 Jan 2023 09:58:36 +0800
From:   Kefeng Wang <wangkefeng.wang@...wei.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
CC:     <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        <willy@...radead.org>
Subject: Re: [PATCH v2] mm: huge_memory: convert split_huge_pages_all() to use
 a folio



On 2022/12/31 5:45, Andrew Morton wrote:
> On Fri, 30 Dec 2022 17:30:20 +0800 Kefeng Wang <wangkefeng.wang@...wei.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?