Peter Xu <peterx@xxxxxxxxxx> writes:
> Introduce per-vma begin()/end() helpers for pgtable walks. This is a
> preparation work to merge hugetlb pgtable walkers with generic mm.
>
> The helpers need to be called before and after a pgtable walk, will start
> to be needed if the pgtable walker code supports hugetlb pages. It's a
> hook point for any type of VMA, but for now only hugetlb uses it to
> stablize the pgtable pages from getting away (due to possible pmd
> unsharing).
>
> Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
> ---
> include/linux/mm.h | 3 +++
> mm/memory.c | 12 ++++++++++++
> 2 files changed, 15 insertions(+)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 64cd1ee4aacc..349232dd20fb 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -4154,4 +4154,7 @@ static inline bool pfn_is_unaccepted_memory(unsigned long pfn)
> return range_contains_unaccepted_memory(paddr, paddr + PAGE_SIZE);
> }
>
> +void vma_pgtable_walk_begin(struct vm_area_struct *vma);
> +void vma_pgtable_walk_end(struct vm_area_struct *vma);
> +
> #endif /* _LINUX_MM_H */
> diff --git a/mm/memory.c b/mm/memory.c
> index e27e2e5beb3f..3a6434b40d87 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -6180,3 +6180,15 @@ void ptlock_free(struct ptdesc *ptdesc)
> kmem_cache_free(page_ptl_cachep, ptdesc->ptl);
> }
> #endif
> +
> +void vma_pgtable_walk_begin(struct vm_area_struct *vma)
> +{
> + if (is_vm_hugetlb_page(vma))
> + hugetlb_vma_lock_read(vma);
> +}
>
That is required only if we support pmd sharing?
> +
> +void vma_pgtable_walk_end(struct vm_area_struct *vma)
> +{
> + if (is_vm_hugetlb_page(vma))
> + hugetlb_vma_unlock_read(vma);
> +}
> --
> 2.41.0
