Re: [PATCH v1 1/4] mm: move vma_kernel_pagesize() from hugetlb to mm.h

["David Hildenbrand (Arm)" <david@kernel.org>]

On 3/6/26 12:07, Lorenzo Stoakes (Oracle) wrote:
> On Fri, Mar 06, 2026 at 11:15:57AM +0100, David Hildenbrand (Arm) wrote:
>> In the past, only hugetlb had special "vma_kernel_pagesize()"
>> requirements, so it provided its own implementation.
>>
>> In commit 05ea88608d4e ("mm, hugetlbfs: introduce ->pagesize() to
>> vm_operations_struct") we generalized that approach by providing a
>> vm_ops->pagesize() callback to be used by device-dax.
>>
>> Once device-dax started using that callback in commit c1d53b92b95c
>> ("device-dax: implement ->pagesize() for smaps to report MMUPageSize")
>> it was missed that CONFIG_DEV_DAX does not depend on hugetlb support.
>>
>> So building a kernel with CONFIG_DEV_DAX but without CONFIG_HUGETLBFS
>> would not pick up that value.
>>
>> Fix it by moving vma_kernel_pagesize() to mm.h, providing only a single
>> implementation. While at it, improve the kerneldoc a bit.
>>
>> Ideally, we'd move vma_mmu_pagesize() as well to the header. However,
>> its __weak symbol might be overwritten by a PPC variant in hugetlb code.
>> So let's leave it in there for now, as it really only matters for some
>> hugetlb oddities.
>>
>> This was found by code inspection.
>>
>> Fixes: c1d53b92b95c ("device-dax: implement ->pagesize() for smaps to report MMUPageSize")
>> Cc: Dan Williams <dan.j.williams@intel.com>
>> Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
> 
> LGTM, but you need to fix up VMA tests, I attach a patch below to do this. Will
> this resolved:

Thanks!

I assume that should go into patch #2 instead?

> 
> Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>


[...]

> ---
>  tools/testing/vma/include/dup.h | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/tools/testing/vma/include/dup.h b/tools/testing/vma/include/dup.h
> index 3078ff1487d3..65b1030a7fdf 100644
> --- a/tools/testing/vma/include/dup.h
> +++ b/tools/testing/vma/include/dup.h
> @@ -1318,3 +1318,10 @@ static inline void vma_set_file(struct vm_area_struct *vma, struct file *file)
>  	swap(vma->vm_file, file);
>  	fput(file);
>  }
> +
> +static inline unsigned long vma_kernel_pagesize(struct vm_area_struct *vma)
> +{
> +	if (unlikely(vma->vm_ops && vma->vm_ops->pagesize))
> +		return vma->vm_ops->pagesize(vma);
> +	return PAGE_SIZE;

Should we just KIS and use PAGE_SIZE for the test?

-- 
Cheers,

David