Re: [PATCH v8 02/10] mm: Non-pmd-mappable, large folios for folio_add_new_anon_rmap()

[Barry Song]

On Mon, Dec 4, 2023 at 6:20 PM Ryan Roberts <ryan.roberts@xxxxxxx> wrote:
>
> In preparation for supporting anonymous multi-size THP, improve
> folio_add_new_anon_rmap() to allow a non-pmd-mappable, large folio to be
> passed to it. In this case, all contained pages are accounted using the
> order-0 folio (or base page) scheme.
>
> Reviewed-by: Yu Zhao <yuzhao@xxxxxxxxxx>
> Reviewed-by: Yin Fengwei <fengwei.yin@xxxxxxxxx>
> Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
> Signed-off-by: Ryan Roberts <ryan.roberts@xxxxxxx>

Reviewed-by: Barry Song <v-songbaohua@xxxxxxxx>

> ---
>  mm/rmap.c | 28 ++++++++++++++++++++--------
>  1 file changed, 20 insertions(+), 8 deletions(-)
>
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 2a1e45e6419f..846fc79f3ca9 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1335,32 +1335,44 @@ void page_add_anon_rmap(struct page *page, struct vm_area_struct *vma,
>   * This means the inc-and-test can be bypassed.
>   * The folio does not have to be locked.
>   *
> - * If the folio is large, it is accounted as a THP.  As the folio
> + * If the folio is pmd-mappable, it is accounted as a THP.  As the folio
>   * is new, it's assumed to be mapped exclusively by a single process.
>   */
>  void folio_add_new_anon_rmap(struct folio *folio, struct vm_area_struct *vma,
>                 unsigned long address)
>  {
> -       int nr;
> +       int nr = folio_nr_pages(folio);
>
> -       VM_BUG_ON_VMA(address < vma->vm_start || address >= vma->vm_end, vma);
> +       VM_BUG_ON_VMA(address < vma->vm_start ||
> +                       address + (nr << PAGE_SHIFT) > vma->vm_end, vma);
>         __folio_set_swapbacked(folio);
> +       __folio_set_anon(folio, vma, address, true);
>
> -       if (likely(!folio_test_pmd_mappable(folio))) {
> +       if (likely(!folio_test_large(folio))) {
>                 /* increment count (starts at -1) */
>                 atomic_set(&folio->_mapcount, 0);
> -               nr = 1;
> +               SetPageAnonExclusive(&folio->page);
> +       } else if (!folio_test_pmd_mappable(folio)) {
> +               int i;
> +
> +               for (i = 0; i < nr; i++) {
> +                       struct page *page = folio_page(folio, i);
> +
> +                       /* increment count (starts at -1) */
> +                       atomic_set(&page->_mapcount, 0);
> +                       SetPageAnonExclusive(page);
> +               }
> +
> +               atomic_set(&folio->_nr_pages_mapped, nr);
>         } else {
>                 /* increment count (starts at -1) */
>                 atomic_set(&folio->_entire_mapcount, 0);
>                 atomic_set(&folio->_nr_pages_mapped, COMPOUND_MAPPED);
> -               nr = folio_nr_pages(folio);
> +               SetPageAnonExclusive(&folio->page);
>                 __lruvec_stat_mod_folio(folio, NR_ANON_THPS, nr);
>         }
>
>         __lruvec_stat_mod_folio(folio, NR_ANON_MAPPED, nr);
> -       __folio_set_anon(folio, vma, address, true);
> -       SetPageAnonExclusive(&folio->page);
>  }
>
>  /**
> --
> 2.25.1
>