Re: [PATCH v2 06/10] mm: avoid using vma_merge() for new VMAs

[Lorenzo Stoakes]

On Fri, Aug 23, 2024 at 09:07:01PM GMT, Lorenzo Stoakes wrote:

[snip]

>  void unlink_file_vma_batch_init(struct unlink_vma_file_batch *vb)
> @@ -1426,9 +1536,10 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
>  	struct vm_area_struct *vma = *vmap;
>  	unsigned long vma_start = vma->vm_start;
>  	struct mm_struct *mm = vma->vm_mm;
> -	struct vm_area_struct *new_vma, *prev;
> +	struct vm_area_struct *new_vma;
>  	bool faulted_in_anon_vma = true;
>  	VMA_ITERATOR(vmi, mm, addr);
> +	VMG_VMA_STATE(vmg, &vmi, NULL, vma, addr, addr + len);
>
>  	/*
>  	 * If anonymous vma has not yet been faulted, update new pgoff
> @@ -1439,11 +1550,18 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
>  		faulted_in_anon_vma = false;
>  	}
>
> -	new_vma = find_vma_prev(mm, addr, &prev);
> +	new_vma = find_vma_prev(mm, addr, &vmg.prev);
>  	if (new_vma && new_vma->vm_start < addr + len)
>  		return NULL;	/* should never get here */
>
> -	new_vma = vma_merge_new_vma(&vmi, prev, vma, addr, addr + len, pgoff);
> +	vmg.vma = NULL; /* New VMA range. */
> +	vmg.pgoff = pgoff;
> +	vmg.next = vma_next(&vmi);
> +	vma_prev(&vmi);
> +	vma_iter_next_range(&vmi);
> +
> +	new_vma = vma_merge_new_range(&vmg);
> +
>  	if (new_vma) {
>  		/*
>  		 * Source vma may have been merged into new_vma

[snip]

Hi Andrew - could you squash the attached fix-patch into this please? As
there is an issue with a CONFIG_DEBUG_VM check firing when copy_vma()
unnecessarily moves the VMA iterator as reported at [0].

Thanks!

[0]: https://lore.kernel.org/linux-mm/202408271452.c842a71d-lkp@xxxxxxxxx/

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