linux-kernel - Re: [PATCH 4/8] mm/rmap: remove anon_vma

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Message-ID: <CAJuCfpFTSAyzHBiz3u599td_A9DrcTjhTi94vE+=V_V0Bkawrg@mail.gmail.com>
Date: Tue, 30 Dec 2025 11:35:02 -0800
From: Suren Baghdasaryan <surenb@...gle.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, "Liam R . Howlett" <Liam.Howlett@...cle.com>, 
	Vlastimil Babka <vbabka@...e.cz>, Shakeel Butt <shakeel.butt@...ux.dev>, 
	David Hildenbrand <david@...nel.org>, Rik van Riel <riel@...riel.com>, Harry Yoo <harry.yoo@...cle.com>, 
	Jann Horn <jannh@...gle.com>, Mike Rapoport <rppt@...nel.org>, Michal Hocko <mhocko@...e.com>, 
	Pedro Falcato <pfalcato@...e.de>, Chris Li <chriscli@...gle.com>, 
	Barry Song <v-songbaohua@...o.com>, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/8] mm/rmap: remove anon_vma_merge() function

On Wed, Dec 17, 2025 at 4:27 AM Lorenzo Stoakes
<lorenzo.stoakes@...cle.com> wrote:
>
> This function is confusing, we already have the concept of anon_vma merge
> to adjacent VMA's anon_vma's to increase probability of anon_vma
> compatibility and therefore VMA merge (see is_mergeable_anon_vma() etc.),
> as well as anon_vma reuse, along side the usual VMA merge logic.
>
> We can remove the anon_vma check as it is redundant - a merge would not
> have been permitted with removal if the anon_vma's were not the same (and
> in the case of an unfaulted/faulted merge, we would have already set the
> unfaulted VMA's anon_vma to vp->remove->anon_vma in dup_anon_vma()).
>
> Avoid overloading this term when we're very simply unlinking anon_vma state
> from a removed VMA upon merge.
>
> Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>

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

> ---
>  include/linux/rmap.h             | 7 -------
>  mm/vma.c                         | 2 +-
>  tools/testing/vma/vma_internal.h | 5 -----
>  3 files changed, 1 insertion(+), 13 deletions(-)
>
> diff --git a/include/linux/rmap.h b/include/linux/rmap.h
> index daa92a58585d..832bfc0ccfc6 100644
> --- a/include/linux/rmap.h
> +++ b/include/linux/rmap.h
> @@ -165,13 +165,6 @@ static inline int anon_vma_prepare(struct vm_area_struct *vma)
>         return __anon_vma_prepare(vma);
>  }
>
> -static inline void anon_vma_merge(struct vm_area_struct *vma,
> -                                 struct vm_area_struct *next)
> -{
> -       VM_BUG_ON_VMA(vma->anon_vma != next->anon_vma, vma);
> -       unlink_anon_vmas(next);
> -}
> -
>  struct anon_vma *folio_get_anon_vma(const struct folio *folio);
>
>  #ifdef CONFIG_MM_ID
> diff --git a/mm/vma.c b/mm/vma.c
> index fc90befd162f..feb4bbd3b259 100644
> --- a/mm/vma.c
> +++ b/mm/vma.c
> @@ -376,7 +376,7 @@ static void vma_complete(struct vma_prepare *vp, struct vma_iterator *vmi,
>                         fput(vp->file);
>                 }
>                 if (vp->remove->anon_vma)
> -                       anon_vma_merge(vp->vma, vp->remove);
> +                       unlink_anon_vmas(vp->remove);
>                 mm->map_count--;
>                 mpol_put(vma_policy(vp->remove));
>                 if (!vp->remove2)
> diff --git a/tools/testing/vma/vma_internal.h b/tools/testing/vma/vma_internal.h
> index 9f0a9f5ed0fe..93e5792306d9 100644
> --- a/tools/testing/vma/vma_internal.h
> +++ b/tools/testing/vma/vma_internal.h
> @@ -1265,11 +1265,6 @@ static inline void i_mmap_unlock_write(struct address_space *mapping)
>  {
>  }
>
> -static inline void anon_vma_merge(struct vm_area_struct *vma,
> -                                 struct vm_area_struct *next)
> -{
> -}
> -
>  static inline int userfaultfd_unmap_prep(struct vm_area_struct *vma,
>                                          unsigned long start,
>                                          unsigned long end,
> --
> 2.52.0