Re: [PATCH v2 4/8] mm/rmap: remove anon_vma_merge() function

["Liam R. Howlett" <Liam.Howlett@oracle.com>]

* Lorenzo Stoakes <lorenzo.stoakes@oracle.com> [260106 10:04]:
> 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@oracle.com>
> Reviewed-by: Suren Baghdasaryan <surenb@google.com>

Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.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 fb45a6be7417..4294ecdc23a5 100644
> --- a/mm/vma.c
> +++ b/mm/vma.c
> @@ -379,7 +379,7 @@ 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
>