linux-kernel - Re: [PATCH v1 1/3] mm/rmap: move SetPageAnonExclusive() out of page_move_anon

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Date:   Tue, 3 Oct 2023 09:55:55 -0700
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Muchun Song <muchun.song@...ux.dev>
Subject: Re: [PATCH v1 1/3] mm/rmap: move SetPageAnonExclusive() out of page_move_anon_rmap()

On Mon, Oct 2, 2023 at 7:29 AM David Hildenbrand <david@...hat.com> wrote:
>
> Let's move it into the caller: there is a difference between whether an
> anon folio can only be mapped by one process (e.g., into one VMA), and
> whether it is truly exclusive (e.g., no references -- including GUP --
> from other processes).
>
> Further, for large folios the page might not actually be pointing at the
> head page of the folio, so it better be handled in the caller. This is a
> preparation for converting page_move_anon_rmap() to consume a folio.
>
> Signed-off-by: David Hildenbrand <david@...hat.com>

Reviewed-by: Suren Baghdasaryan <surenb@...gle.com>

> ---
>  mm/huge_memory.c | 1 +
>  mm/hugetlb.c     | 4 +++-
>  mm/memory.c      | 1 +
>  mm/rmap.c        | 1 -
>  4 files changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index e54fb9c542bb..01d0d65ece13 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -1506,6 +1506,7 @@ vm_fault_t do_huge_pmd_wp_page(struct vm_fault *vmf)
>                 pmd_t entry;
>
>                 page_move_anon_rmap(page, vma);
> +               SetPageAnonExclusive(page);
>                 folio_unlock(folio);
>  reuse:
>                 if (unlikely(unshare)) {
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 9c22297d9c57..24591fc145ff 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -5460,8 +5460,10 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
>          * owner and can reuse this page.
>          */
>         if (folio_mapcount(old_folio) == 1 && folio_test_anon(old_folio)) {
> -               if (!PageAnonExclusive(&old_folio->page))
> +               if (!PageAnonExclusive(&old_folio->page)) {
>                         page_move_anon_rmap(&old_folio->page, vma);
> +                       SetPageAnonExclusive(&old_folio->page);
> +               }
>                 if (likely(!unshare))
>                         set_huge_ptep_writable(vma, haddr, ptep);
>
> diff --git a/mm/memory.c b/mm/memory.c
> index d4820802b01b..9de231c92769 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3484,6 +3484,7 @@ static vm_fault_t do_wp_page(struct vm_fault *vmf)
>                  * sunglasses. Hit it.
>                  */
>                 page_move_anon_rmap(vmf->page, vma);
> +               SetPageAnonExclusive(vmf->page);
>                 folio_unlock(folio);
>  reuse:
>                 if (unlikely(unshare)) {
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 77222adccda1..854ccbd66954 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1165,7 +1165,6 @@ void page_move_anon_rmap(struct page *page, struct vm_area_struct *vma)
>          * folio_test_anon()) will not see one without the other.
>          */
>         WRITE_ONCE(folio->mapping, anon_vma);
> -       SetPageAnonExclusive(page);
>  }
>
>  /**
> --
> 2.41.0
>