Re: [PATCH v10 2/8] mm/huge_memory: add two new (not yet used) functions for folio_split()

[Matthew Wilcox]

On Fri, Mar 07, 2025 at 12:39:55PM -0500, Zi Yan wrote:
> +	for (index = new_nr_pages; index < nr_pages; index += new_nr_pages) {
> +		struct page *head = &folio->page;
> +		struct page *new_head = head + index;
> +
> +		/*
> +		 * Careful: new_folio is not a "real" folio before we cleared PageTail.
> +		 * Don't pass it around before clear_compound_head().
> +		 */
> +		struct folio *new_folio = (struct folio *)new_head;
[...]
> +		/* ->mapping in first and second tail page is replaced by other uses */
> +		VM_BUG_ON_PAGE(new_nr_pages > 2 && new_head->mapping != TAIL_MAPPING,
> +			       new_head);
> +		new_head->mapping = head->mapping;
> +		new_head->index = head->index + index;

Why are you using new_head->mapping and ->index instead of new_folio?