linux-kernel - Re: [RFC PATCH v2] page_alloc: allow migration of smaller hugepages during contig

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Message-ID: <20251021201513.kxhjiirr4nmzaw7u@master>
Date: Tue, 21 Oct 2025 20:15:13 +0000
From: Wei Yang <richard.weiyang@...il.com>
To: Gregory Price <gourry@...rry.net>
Cc: Wei Yang <richard.weiyang@...il.com>, Zi Yan <ziy@...dia.com>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	kernel-team@...a.com, akpm@...ux-foundation.org, vbabka@...e.cz,
	surenb@...gle.com, mhocko@...e.com, jackmanb@...gle.com,
	hannes@...xchg.org, David Hildenbrand <david@...hat.com>
Subject: Re: [RFC PATCH v2] page_alloc: allow migration of smaller hugepages
 during contig_alloc

On Tue, Oct 21, 2025 at 12:03:39PM -0400, Gregory Price wrote:
>On Tue, Oct 21, 2025 at 09:14:43AM +0000, Wei Yang wrote:
>> 
>> The above code is expanded to:
>> 
>>   page = _compound_head(page);
>>   order = compound_order(page);
>>       folio = page;
>>       test_bit(PG_head, &folio->flags.f);
>>       return folio_large_order(folio);
>> 
>> If we use
>> 
>>   order = folio_order(page_folio(page))
>> 
>> It is expanded to:
>> 
>>   folio = _compound_head(page);
>>   folio_test_large(folio)
>>       folio_test_head(folio)
>>           test_bit(PG_head, &folio->flags.f)
>>   return folio_large_order(folio);
>> 
>> These two seems expanded to the same code.
>> 
>
>folio_test_large drops into const_folio_flags which does
>a VM_BUG_ON_PGFLAGS, so not the same logic here.
>

Thanks, you are right.

>> Maybe we can use folio_order() here?
>> 

-- 
Wei Yang
Help you, Help me