Re: [PATCH 25/30] mm/vma: update vmg_adjust_set_range() to offset pgoff instead

[Pedro Falcato]

On Mon, Jun 29, 2026 at 01:23:36PM +0100, Lorenzo Stoakes wrote:
> We are calculating the pgoff as an offset, since we have vma_add_pgoff()
> and vma_sub_pgoff() available, just offset this value directly and use
> __vma_set_range() for vma->vm_[start, end] values.
> 
> We take care to update the range before offsetting the page offset, so the
> adjusted VMA's vm_start and vm_pgoff are mutually consistent at the point
> the page offset helpers operate - this matters once vma_set_pgoff() comes
> to assert invariants which relate the two.
> 
> Doing so lays the foundation for future work which allows for use of
> virtual page offsets for MAP_PRIVATE-file backed mappings.
> 
> No functional change intended.
> 
> Signed-off-by: Lorenzo Stoakes <ljs@xxxxxxxxxx>
> ---
>  mm/vma.c | 15 ++++-----------
>  1 file changed, 4 insertions(+), 11 deletions(-)
> 
> diff --git a/mm/vma.c b/mm/vma.c
> index e3355eab11f2..0579fc8c9bd5 100644
> --- a/mm/vma.c
> +++ b/mm/vma.c
> @@ -714,9 +714,6 @@ void validate_mm(struct mm_struct *mm)
>   */
>  static void vmg_adjust_set_range(struct vma_merge_struct *vmg)
>  {
> -	struct vm_area_struct *adjust;
> -	pgoff_t pgoff;
> -
>  	if (vmg->__adjust_middle_start) {
>  		/*
>  		 * vmg->start    vmg->end
> @@ -735,8 +732,8 @@ static void vmg_adjust_set_range(struct vma_merge_struct *vmg)
>  		struct vm_area_struct *middle = vmg->middle;
>  		const unsigned long delta = vmg->end - middle->vm_start;
>  
> -		pgoff = vma_start_pgoff(middle) + (delta >> PAGE_SHIFT);
> -		adjust = middle;
> +		__vma_set_range(middle, vmg->end, middle->vm_end);
> +		vma_add_pgoff(middle, delta >> PAGE_SHIFT);
>  	} else if (vmg->__adjust_next_start) {
>  		/*
>  		 *                Originally:
> @@ -764,13 +761,9 @@ static void vmg_adjust_set_range(struct vma_merge_struct *vmg)
>  		struct vm_area_struct *next = vmg->next;
>  		const unsigned long delta = next->vm_start - vmg->end;
>  
> -		pgoff = vma_start_pgoff(next) - (delta >> PAGE_SHIFT);
> -		adjust = next;
> -	} else {
> -		return;
> +		__vma_set_range(next, vmg->end, next->vm_end);
> +		vma_sub_pgoff(next, delta >> PAGE_SHIFT);
>  	}
> -
> -	vma_set_range(adjust, vmg->end, adjust->vm_end, pgoff);
>  }

Maybe this should be squashed with That Other Patch that touches this.

Anyway,

Reviewed-by: Pedro Falcato <pfalcato@xxxxxxx> 

-- 
Pedro