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

Lorenzo Stoakes (Oracle)
2026-03-06T11:07:45Z

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:

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

> ---
> include/linux/hugetlb.h | 7 -------
> include/linux/mm.h | 20 ++++++++++++++++++++
> mm/hugetlb.c | 17 -----------------
> 3 files changed, 20 insertions(+), 24 deletions(-)
>
> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index 65910437be1c..44c1848a2c21 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -777,8 +777,6 @@ static inline unsigned long huge_page_size(const struct hstate *h)
> return (unsigned long)PAGE_SIZE << h->order;
> }
>
> -extern unsigned long vma_kernel_pagesize(struct vm_area_struct *vma);
> -
> extern unsigned long vma_mmu_pagesize(struct vm_area_struct *vma);
>
> static inline unsigned long huge_page_mask(struct hstate *h)
> @@ -1177,11 +1175,6 @@ static inline unsigned long huge_page_mask(struct hstate *h)
> return PAGE_MASK;
> }
>
> -static inline unsigned long vma_kernel_pagesize(struct vm_area_struct *vma)
> -{
> - return PAGE_SIZE;
> -}
> -
> static inline unsigned long vma_mmu_pagesize(struct vm_area_struct *vma)
> {
> return PAGE_SIZE;
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 44e04a42fe77..227809790f1a 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1307,6 +1307,26 @@ static inline bool vma_is_shared_maywrite(const struct vm_area_struct *vma)
> return is_shared_maywrite(&vma->flags);
> }
>
> +/**
> + * vma_kernel_pagesize - Default page size granularity for this VMA.
> + * @vma: The user mapping.
> + *
> + * The kernel page size specifies in which granularity VMA modifications
> + * can be performed. Folios in this VMA will be aligned to, and at least
> + * the size of the number of bytes returned by this function.
> + *
> + * The default kernel page size is not affected by Transparent Huge Pages
> + * being in effect.
> + *
> + * Return: The default page size granularity for this VMA.
> + */
> +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;
> +}
> +
> static inline
> struct vm_area_struct *vma_find(struct vma_iterator *vmi, unsigned long max)
> {
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 1d41fa3dd43e..66eadfa9e958 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1017,23 +1017,6 @@ static pgoff_t vma_hugecache_offset(struct hstate *h,
> (vma->vm_pgoff >> huge_page_order(h));
> }
>
> -/**
> - * vma_kernel_pagesize - Page size granularity for this VMA.
> - * @vma: The user mapping.
> - *
> - * Folios in this VMA will be aligned to, and at least the size of the
> - * number of bytes returned by this function.
> - *
> - * Return: The default size of the folios allocated when backing a VMA.
> - */
> -unsigned long vma_kernel_pagesize(struct vm_area_struct *vma)
> -{
> - if (vma->vm_ops && vma->vm_ops->pagesize)
> - return vma->vm_ops->pagesize(vma);
> - return PAGE_SIZE;
> -}
> -EXPORT_SYMBOL_GPL(vma_kernel_pagesize);
> -
> /*
> * Return the page size being used by the MMU to back a VMA. In the majority
> * of cases, the page size used by the kernel matches the MMU size. On
> --
> 2.43.0
>

----8<----
This breaks the VMA tests when patch 2/4 removes the references in other
headers. So this patch should also update them, I enclose a simple fix for
convenience:

From bec84895cbdbe28e3495c4d90e097074598419e5 Mon Sep 17 00:00:00 2001
From: "Lorenzo Stoakes (Oracle)" <ljs@kernel.org>
Date: Fri, 6 Mar 2026 11:05:12 +0000
Subject: [PATCH] fix

---
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;
+}
--
2.53.0