Re: [PATCH v2 20/46] mm/migrate: Add folio_migrate_copy()

[Christoph Hellwig]

> +void folio_migrate_copy(struct folio *newfolio, struct folio *folio)
>  {
> +	unsigned int i = folio_nr_pages(folio) - 1;
>  
> +	copy_highpage(folio_page(newfolio, i), folio_page(folio, i));
> +	while (i-- > 0) {
> +		cond_resched()a
> +		/* folio_page() handles discontinuities in memmap */
> +		copy_highpage(folio_page(newfolio, i), folio_page(folio, i));
> +	}
> +

What is the advantage of copying backwards here to start with?