On 10 Mar 2025, at 12:30, Matthew Wilcox wrote:
> 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?
Because of the “Careful” comment. But new_folio->* should be fine,
since it is the same as new_head. So I probably can replace all
new_head with new_folio except those VM_BUG_ON_PAGE checks?
Best Regards,
Yan, Zi
