Re: [PATCH v1 04/39] mm/rmap: introduce and use hugetlb_try_dup_anon_rmap()

Ryan Roberts
2023-12-11T16:25:58Z

On 11/12/2023 15:56, David Hildenbrand wrote:
> hugetlb rmap handling differs quite a lot from "ordinary" rmap code.
> For example, hugetlb currently only supports entire mappings, and treats
> any mapping as mapped using a single "logical PTE". Let's move it out
> of the way so we can overhaul our "ordinary" rmap.
> implementation/interface.
>
> So let's introduce and use hugetlb_try_dup_anon_rmap() to make all
> hugetlb handling use dedicated hugetlb_* rmap functions.
>
> Note that is_device_private_page() does not apply to hugetlb.
>
> Reviewed-by: Yin Fengwei <fengwei.yin@intel.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>

Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>

> ---
> include/linux/mm.h | 12 +++++++++---
> include/linux/rmap.h | 15 +++++++++++++++
> mm/hugetlb.c | 3 +--
> 3 files changed, 25 insertions(+), 5 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index b72bf25a45cf..ae547b62f325 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1964,15 +1964,21 @@ static inline bool page_maybe_dma_pinned(struct page *page)
> *
> * The caller has to hold the PT lock and the vma->vm_mm->->write_protect_seq.
> */
> -static inline bool page_needs_cow_for_dma(struct vm_area_struct *vma,
> - struct page *page)
> +static inline bool folio_needs_cow_for_dma(struct vm_area_struct *vma,
> + struct folio *folio)
> {
> VM_BUG_ON(!(raw_read_seqcount(&vma->vm_mm->write_protect_seq) & 1));
>
> if (!test_bit(MMF_HAS_PINNED, &vma->vm_mm->flags))
> return false;
>
> - return page_maybe_dma_pinned(page);
> + return folio_maybe_dma_pinned(folio);
> +}
> +
> +static inline bool page_needs_cow_for_dma(struct vm_area_struct *vma,
> + struct page *page)
> +{
> + return folio_needs_cow_for_dma(vma, page_folio(page));
> }
>
> /**
> diff --git a/include/linux/rmap.h b/include/linux/rmap.h
> index 91178d1aa028..ca42b3db5688 100644
> --- a/include/linux/rmap.h
> +++ b/include/linux/rmap.h
> @@ -213,6 +213,21 @@ void hugetlb_add_anon_rmap(struct folio *, struct vm_area_struct *,
> void hugetlb_add_new_anon_rmap(struct folio *, struct vm_area_struct *,
> unsigned long address);
>
> +/* See page_try_dup_anon_rmap() */
> +static inline int hugetlb_try_dup_anon_rmap(struct folio *folio,
> + struct vm_area_struct *vma)
> +{
> + VM_WARN_ON_FOLIO(!folio_test_anon(folio), folio);
> +
> + if (PageAnonExclusive(&folio->page)) {
> + if (unlikely(folio_needs_cow_for_dma(vma, folio)))
> + return -EBUSY;
> + ClearPageAnonExclusive(&folio->page);
> + }
> + atomic_inc(&folio->_entire_mapcount);
> + return 0;
> +}
> +
> static inline void hugetlb_add_file_rmap(struct folio *folio)
> {
> VM_WARN_ON_FOLIO(folio_test_anon(folio), folio);
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 57e898187931..378e460a6ab4 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -5409,8 +5409,7 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
> */
> if (!folio_test_anon(pte_folio)) {
> hugetlb_add_file_rmap(pte_folio);
> - } else if (page_try_dup_anon_rmap(&pte_folio->page,
> - true, src_vma)) {
> + } else if (hugetlb_try_dup_anon_rmap(pte_folio, src_vma)) {
> pte_t src_pte_old = entry;
> struct folio *new_folio;
>