linux-kernel - Re: [RFC 07/10] treewide: rename has_transparent_hugepage() to arch_has_pmd

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Message-ID: <65b0c614-e6a9-4535-9d30-bd2be7a72149@redhat.com>
Date: Mon, 17 Nov 2025 14:01:49 -0500
From: Luiz Capitulino <luizcap@...hat.com>
To: "David Hildenbrand (Red Hat)" <david@...nel.org>,
 linux-kernel@...r.kernel.org, linux-mm@...ck.org
Cc: ryan.roberts@....com, akpm@...ux-foundation.org,
 lorenzo.stoakes@...cle.com
Subject: Re: [RFC 07/10] treewide: rename has_transparent_hugepage() to
 arch_has_pmd_leaves()

On 2025-11-17 12:45, David Hildenbrand (Red Hat) wrote:
> On 06.11.25 22:28, Luiz Capitulino wrote:
>> Now that the majority of has_transparent_hugepage() callers have been
>> converted to pgtable_has_pmd_leaves(), rename has_transparent_hugepage()
>> to arch_has_pmd_leaves() since that's what the helper checks for.
>>
>> arch_has_pmd_leaves() is supposed to be called only by
>> init_arch_has_pmd_leaves(), except for two exeptions:
>>
>> 1. shmem: shmem code runs very early during boot so it can't use
>>     pgtable_has_pmd_leaves()
> 
> Can't we just initialize pgtable_has_pmd_leaves() earlier then?

I can look into doing that. When I worked on this RFC I wondered if
arch_has_pmd_leaves() (when implemented by the arch) could run so early
given that some (all?) archs check feature bits so they must be
available this early as well. But I'll check this, having
pgtable_has_pmd_leaves() being available as early as possible is
probably the right thing to do.

>> 2. hugepage_init(): just a temporary exception, this function will be
>>     converted in a future commit
>>
>> Signed-off-by: Luiz Capitulino <luizcap@...hat.com>
>> ---
> 
> 
> [...]
> 
>> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
>> index e4c5f70b0a01..02a2772ec548 100644
>> --- a/include/linux/pgtable.h
>> +++ b/include/linux/pgtable.h
>> @@ -2026,8 +2026,8 @@ static inline bool pgtable_has_pmd_leaves(void)
>>   #endif
>>   #endif
>> -#ifndef has_transparent_hugepage
>> -#define has_transparent_hugepage() IS_BUILTIN(CONFIG_TRANSPARENT_HUGEPAGE)
>> +#ifndef arch_has_pmd_leaves
>> +#define arch_has_pmd_leaves() IS_BUILTIN(CONFIG_TRANSPARENT_HUGEPAGE)
>>   #endif
> 
> Ah, so it stays for now only set with CONFIG_TRANSPARENT_HUGEPAGE. I guess that's something to sort out later :)

I suggested something we could do in this series. Also, I skipped
commenting on all the cases you spotted as I think they refer to the
same issue (please, do point out if you think I'm wrong).