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

["Lorenzo Stoakes (Oracle)" <ljs@kernel.org>]

On Fri, Mar 06, 2026 at 02:25:51PM +0100, David Hildenbrand (Arm) wrote:
> 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?

Yeah that's fine, but then should go in tools/testing/vma/include/custom.h :>)

I tidied things up there to make it easier to understand WTH is going on with
the headers used by VMA tests.

>
> --
> Cheers,
>
> David

Thanks, Lorenzo