On 5/11/21 11:47 PM, Matthew Wilcox (Oracle) wrote:

+/**
+ * folio_page - Return a page from a folio.
+ * @folio: The folio.
+ * @n: The page number to return.
+ *
+ * @n is relative to the start of the folio.  It should be between
+ * 0 and folio_nr_pages(@folio) - 1, but this is not checked for.
+ */
+#define folio_page(folio, n)	nth_page(&(folio)->page, n)

BTW, would it make sense to have also a folio_page(folio) wrapper? Or is
"&folio->page" used in later patches sufficiently elegant and stable enough for
the future?

 static __always_inline int PageTail(struct page *page)
 {
 	return READ_ONCE(page->compound_head) & 1;