Re: [PATCH v1 04/10] mm: Implement folio_add_new_anon_rmap_range()

[Yu Zhao <yuzhao@google.com>]

On Mon, Jun 26, 2023 at 11:14 AM Ryan Roberts <ryan.roberts@arm.com> wrote:
>
> Like folio_add_new_anon_rmap() but batch-rmaps a range of pages
> belonging to a folio, for effciency savings. All pages are accounted as
> small pages.
>
> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
> ---
>  include/linux/rmap.h |  2 ++
>  mm/rmap.c            | 43 +++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 45 insertions(+)
>
> diff --git a/include/linux/rmap.h b/include/linux/rmap.h
> index a3825ce81102..15433a3d0cbf 100644
> --- a/include/linux/rmap.h
> +++ b/include/linux/rmap.h
> @@ -196,6 +196,8 @@ void page_add_new_anon_rmap(struct page *, struct vm_area_struct *,
>                 unsigned long address);
>  void folio_add_new_anon_rmap(struct folio *, struct vm_area_struct *,
>                 unsigned long address);
> +void folio_add_new_anon_rmap_range(struct folio *folio, struct page *page,
> +               int nr, struct vm_area_struct *vma, unsigned long address);

We should update folio_add_new_anon_rmap() to support large() &&
!folio_test_pmd_mappable() folios instead.

I double checked all places currently using folio_add_new_anon_rmap(),
and as expected, none actually allocates large() &&
!folio_test_pmd_mappable() and maps it one by one, which makes the
cases simpler, i.e.,
  if (!large())
    // the existing basepage case
  else if (!folio_test_pmd_mappable())
    // our new case
  else
    // the existing THP case

>  void page_add_file_rmap(struct page *, struct vm_area_struct *,
>                 bool compound);
>  void folio_add_file_rmap_range(struct folio *, struct page *, unsigned int nr,
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 1d8369549424..4050bcea7ae7 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1305,6 +1305,49 @@ void folio_add_new_anon_rmap(struct folio *folio, struct vm_area_struct *vma,
>         __page_set_anon_rmap(folio, &folio->page, vma, address, 1);
>  }
>
> +/**
> + * folio_add_new_anon_rmap_range - Add mapping to a set of pages within a new
> + * anonymous potentially large folio.
> + * @folio:      The folio containing the pages to be mapped
> + * @page:       First page in the folio to be mapped
> + * @nr:         Number of pages to be mapped
> + * @vma:        the vm area in which the mapping is added
> + * @address:    the user virtual address of the first page to be mapped
> + *
> + * Like folio_add_new_anon_rmap() but batch-maps a range of pages within a folio
> + * using non-THP accounting. Like folio_add_new_anon_rmap(), the inc-and-test is
> + * bypassed and the folio does not have to be locked. All pages in the folio are
> + * individually accounted.
> + *
> + * As the folio is new, it's assumed to be mapped exclusively by a single
> + * process.
> + */
> +void folio_add_new_anon_rmap_range(struct folio *folio, struct page *page,
> +               int nr, struct vm_area_struct *vma, unsigned long address)
> +{
> +       int i;
> +
> +       VM_BUG_ON_VMA(address < vma->vm_start ||
> +                     address + (nr << PAGE_SHIFT) > vma->vm_end, vma);

BTW, VM_BUG_ON* shouldn't be used in new code:
Documentation/process/coding-style.rst