linux-kernel - Re: [RFC 04/10] drivers: i915 selftest: use pgtable_has_pmd

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Message-ID: <21386400-9a67-4fcf-b686-1e7c9678d123@redhat.com>
Date: Mon, 17 Nov 2025 13:55:15 -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 04/10] drivers: i915 selftest: use pgtable_has_pmd_leaves()

On 2025-11-17 12:30, David Hildenbrand (Red Hat) wrote:
> On 06.11.25 22:28, Luiz Capitulino wrote:
>> igt_can_allocate_thp() uses has_transparente_hugepage() to check if
>> PMD-sized pages are supported, use pgtable_has_pmd_leaves() instead.
>>
>> Signed-off-by: Luiz Capitulino <luizcap@...hat.com>
>> ---
>>   drivers/gpu/drm/i915/gem/selftests/huge_pages.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/i915/gem/selftests/huge_pages.c b/drivers/gpu/drm/i915/gem/selftests/huge_pages.c
>> index bd08605a1611..c76aafa36d2b 100644
>> --- a/drivers/gpu/drm/i915/gem/selftests/huge_pages.c
>> +++ b/drivers/gpu/drm/i915/gem/selftests/huge_pages.c
>> @@ -1316,7 +1316,7 @@ typedef struct drm_i915_gem_object *
>>   static inline bool igt_can_allocate_thp(struct drm_i915_private *i915)
>>   {
>> -    return i915->mm.gemfs && has_transparent_hugepage();
>> +    return i915->mm.gemfs && pgtable_has_pmd_leaves();
> 
> On second thought, is it problematic that we might be losing the CONFIG_TRANSPARENT_HUGEPAGE check? Should we check for that separately?

That's a good point.

In this RFC, pgtable_has_pmd_leaves() should be functionally equivalent
to has_transparent_hugepage() so I think we're good. That beind said, I
also think that we should disentangle pgtable_has_pmd_leaves() from THP
now or in the future. When we do this the breakage you're spotting will
happen.

What about adding thp_has_pmd_support() which does:

   return IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) && pgtable_has_pmd_leaves();

Then I can convert all the cases you spotted to thp_has_pmd_support().