readahead: convert readahead_expand() to use a folio

Replace the uses of page with a folio.  Also add a missing test for
workingset in the leading edge expansion.

Link: https://lkml.kernel.org/r/20230116193941.2148487-4-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/readahead.c

@@ -801,21 +801,25 @@ void readahead_expand(struct readahead_control *ractl,
 	/* Expand the leading edge downwards */
 	while (ractl->_index > new_index) {
 		unsigned long index = ractl->_index - 1;
-		struct page *page = xa_load(&mapping->i_pages, index);
+		struct folio *folio = xa_load(&mapping->i_pages, index);
 
-		if (page && !xa_is_value(page))
-			return; /* Page apparently present */
+		if (folio && !xa_is_value(folio))
+			return; /* Folio apparently present */
 
-		page = __page_cache_alloc(gfp_mask);
-		if (!page)
+		folio = filemap_alloc_folio(gfp_mask, 0);
+		if (!folio)
 			return;
-		if (add_to_page_cache_lru(page, mapping, index, gfp_mask) < 0) {
-			put_page(page);
+		if (filemap_add_folio(mapping, folio, index, gfp_mask) < 0) {
+			folio_put(folio);
 			return;
 		}
-
+		if (unlikely(folio_test_workingset(folio)) &&
+				!ractl->_workingset) {
+			ractl->_workingset = true;
+			psi_memstall_enter(&ractl->_pflags);
+		}
 		ractl->_nr_pages++;
-		ractl->_index = page->index;
+		ractl->_index = folio->index;
 	}
 
 	new_len += new_start - readahead_pos(ractl);
@@ -824,19 +828,20 @@ void readahead_expand(struct readahead_control *ractl,
 	/* Expand the trailing edge upwards */
 	while (ractl->_nr_pages < new_nr_pages) {
 		unsigned long index = ractl->_index + ractl->_nr_pages;
-		struct page *page = xa_load(&mapping->i_pages, index);
+		struct folio *folio = xa_load(&mapping->i_pages, index);
 
-		if (page && !xa_is_value(page))
-			return; /* Page apparently present */
+		if (folio && !xa_is_value(folio))
+			return; /* Folio apparently present */
 
-		page = __page_cache_alloc(gfp_mask);
-		if (!page)
+		folio = filemap_alloc_folio(gfp_mask, 0);
+		if (!folio)
 			return;
-		if (add_to_page_cache_lru(page, mapping, index, gfp_mask) < 0) {
-			put_page(page);
+		if (filemap_add_folio(mapping, folio, index, gfp_mask) < 0) {
+			folio_put(folio);
 			return;
 		}
-		if (unlikely(PageWorkingset(page)) && !ractl->_workingset) {
+		if (unlikely(folio_test_workingset(folio)) &&
+				!ractl->_workingset) {
 			ractl->_workingset = true;
 			psi_memstall_enter(&ractl->_pflags);
 		}