On Sat, Mar 13, 2021 at 12:37:16PM -0800, Andrew Morton wrote:

On Fri,  5 Mar 2021 04:18:45 +0000 "Matthew Wilcox (Oracle)" [off-list ref] wrote:

quoted

folio_index() is the equivalent of page_index() for folios.  folio_page()
finds the page in a folio for a page cache index.  folio_contains()
tells you whether a folio contains a particular page cache index.

copy-paste changelog into each function's covering comment?

Certainly.

quoted

+static inline struct page *folio_page(struct folio *folio, pgoff_t index)
+{
+	index -= folio_index(folio);
+	VM_BUG_ON_FOLIO(index >= folio_nr_pages(folio), folio);
+	return &folio->page + index;
+}

One would expect folio_page() to be the reverse of page_folio(), only
it isn't anything like that.

It is ... but only for files.  So maybe folio_file_page()?