Re: [PATCH v4 3/9] drivers: dax: use pgtable_has_pmd_leaves()

[Luiz Capitulino <luizcap@redhat.com>]

On 2026-05-13 11:40, David Hildenbrand (Arm) wrote:
> On 5/1/26 21:18, Luiz Capitulino wrote:
>> dax_align_valid() uses has_transparent_hugepage() to check if PMD-sized
>> pages are supported, use pgtable_has_pmd_leaves() instead.
>>
>> Acked-by: David Hildenbrand (Red Hat) <david@kernel.org>
>> Signed-off-by: Luiz Capitulino <luizcap@redhat.com>
>> ---
>>   drivers/dax/dax-private.h | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/dax/dax-private.h b/drivers/dax/dax-private.h
>> index 81e4af49e39c..35744ff6592a 100644
>> --- a/drivers/dax/dax-private.h
>> +++ b/drivers/dax/dax-private.h
>> @@ -123,7 +123,7 @@ static inline bool dax_align_valid(unsigned long align)
>>   {
>>   	if (align == PUD_SIZE && IS_ENABLED(CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD))
>>   		return true;
>> -	if (align == PMD_SIZE && has_transparent_hugepage())
>> +	if (align == PMD_SIZE && pgtable_has_pmd_leaves())
>>   		return true;
> 
> I think this code really depends on the implied CONFIG_TRANSPARENT_HUGEPAGE check.
> 
> For now, should we just keep saying that pgtable_has_pmd_leaves() implies
> CONFIG_TRANSPARENT_HUGEPAGE support?

Yes, my thinking is that any caller that wants to use PMD-sized pages
with THP, should check for CONFIG_TRANSPARENT_HUGEPAGE. The way we're
doing this in this series is to add a call to
IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) when calling
pgtable_has_pmd_leaves() (the interesting thing is that some
has_transparent_hugepage() callers were doing it already) or rely on
already existing guards like this case.

Btw, in a previous conversation I suggested a wrapper for this case
(say pgtable_has_pmd_thp()) but you didn't like it :)

> 
> That would also e.g., make patch #4 easier.
>