Re: [PATCH RFC 04/12] mm: Introduce vma_pgtable_walk_{begin|end}()

[Aneesh Kumar K.V (IBM) <aneesh.kumar@kernel.org>]

Peter Xu <peterx@redhat.com> 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@redhat.com>
> ---
>  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