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

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Message-ID: <2149802c-b7cd-430c-8af0-99d26b0b7330@kernel.org>
Date: Tue, 2 Dec 2025 11:51:00 +0100
From: "David Hildenbrand (Red Hat)" <david@...nel.org>
To: Luiz Capitulino <luizcap@...hat.com>, 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 11/17/25 19:55, Luiz Capitulino wrote:
> 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().

I hope we can avoid such a wrapper for the time being. Maybe we can just 
keep pgtable_has_pmd_leaves() glued to CONFIG_TRANSPARENT_HUGEPAGE for 
now, and leave untangling that for the next cleanup?

-- 
Cheers

David