Re: [PATCH v2 2/2] mm/mmap: remove find_vma_intersection() in vma_merge()

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

* Yajun Deng <yajun.deng@linux.dev> [240124 22:50]:
> We need to find the current vma by find_vma_intersection() in
> vma_merge(). Since the src vma was passed, we can add a check to figure
> out if the current vma is NULL or the src vma directly.
> 
> Remove find_vma_intersection() in vma_merge(). And initialize the next to
> NULL when defining it.
> 
> Signed-off-by: Yajun Deng <yajun.deng@linux.dev>

Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>

> ---
>  mm/mmap.c | 15 +++++++++------
>  1 file changed, 9 insertions(+), 6 deletions(-)
> 
> diff --git a/mm/mmap.c b/mm/mmap.c
> index f19bc53bc08e..ea02fdc91aa2 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -869,7 +869,7 @@ static struct vm_area_struct
>  	struct mm_struct *mm = src->vm_mm;
>  	struct anon_vma *anon_vma = src->anon_vma;
>  	struct file *file = src->vm_file;
> -	struct vm_area_struct *curr, *next, *res;
> +	struct vm_area_struct *curr = src, *next = NULL, *res;
>  	struct vm_area_struct *vma, *adjust, *remove, *remove2;
>  	struct vm_area_struct *anon_dup = NULL;
>  	struct vma_prepare vp;
> @@ -890,14 +890,18 @@ static struct vm_area_struct
>  	if (vm_flags & VM_SPECIAL)
>  		return NULL;
>  
> -	/* Does the input range span an existing VMA? (cases 5 - 8) */
> -	curr = find_vma_intersection(mm, prev ? prev->vm_end : 0, end);
> +	/*
> +	 * If the current vma and the prev vma are the same vma, it
> +	 * means the current vma is NULL.
> +	 * Does the input range span an existing VMA? (cases 5 - 8)
> +	 */
> +	if (prev == curr || addr != curr->vm_start || end > curr->vm_end)
> +		curr = NULL;
>  
>  	if (!curr ||			/* cases 1 - 4 */
>  	    end == curr->vm_end)	/* cases 6 - 8, adjacent VMA */
>  		next = vma_lookup(mm, end);
> -	else
> -		next = NULL;		/* case 5 */
> +					/* case 5 set to NULL above */
>  
>  	if (prev) {
>  		vma_start = prev->vm_start;
> @@ -921,7 +925,6 @@ static struct vm_area_struct
>  
>  	/* Verify some invariant that must be enforced by the caller. */
>  	VM_WARN_ON(prev && addr <= prev->vm_start);
> -	VM_WARN_ON(curr && (addr != curr->vm_start || end > curr->vm_end));
>  	VM_WARN_ON(addr >= end);
>  
>  	if (!merge_prev && !merge_next)
> -- 
> 2.25.1
>