filemap: Convert find_get_pages_contig to folios

None of the callers of find_get_pages_contig() want tail pages.  They all
use order-0 pages today, but if they were converted, they'd want folios.
So just remove the call to find_subpage() instead of replacing it with
folio_page().
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>

mm/filemap.c

@@ -2208,36 +2208,35 @@ unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t index,
 			       unsigned int nr_pages, struct page **pages)
 {
 	XA_STATE(xas, &mapping->i_pages, index);
-	struct page *page;
+	struct folio *folio;
 	unsigned int ret = 0;
 
 	if (unlikely(!nr_pages))
 		return 0;
 
 	rcu_read_lock();
-	for (page = xas_load(&xas); page; page = xas_next(&xas)) {
-		if (xas_retry(&xas, page))
+	for (folio = xas_load(&xas); folio; folio = xas_next(&xas)) {
+		if (xas_retry(&xas, folio))
 			continue;
 		/*
 		 * If the entry has been swapped out, we can stop looking.
 		 * No current caller is looking for DAX entries.
 		 */
-		if (xa_is_value(page))
+		if (xa_is_value(folio))
 			break;
 
-		if (!page_cache_get_speculative(page))
+		if (!folio_try_get_rcu(folio))
 			goto retry;
 
-		/* Has the page moved or been split? */
-		if (unlikely(page != xas_reload(&xas)))
+		if (unlikely(folio != xas_reload(&xas)))
 			goto put_page;
 
-		pages[ret] = find_subpage(page, xas.xa_index);
+		pages[ret] = &folio->page;
 		if (++ret == nr_pages)
 			break;
 		continue;
 put_page:
-		put_page(page);
+		folio_put(folio);
 retry:
 		xas_reset(&xas);
 	}