writeback: Remove writeback_use_writepage()

The ->writepage operation has been removed from all filesystems but
shmem and swap, neither of which call in here.  Remove this alternative
to calling ->writepages.

Signed-off-by: "Matthew Wilcox (Oracle)" <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Christian Brauner <[email protected]>

Author: Matthew Wilcox (Oracle)

mm/page-writeback.c

@@ -2621,27 +2621,6 @@ int write_cache_pages(struct address_space *mapping,
 }
 EXPORT_SYMBOL(write_cache_pages);
 
-static int writeback_use_writepage(struct address_space *mapping,
-		struct writeback_control *wbc)
-{
-	struct folio *folio = NULL;
-	struct blk_plug plug;
-	int err;
-
-	blk_start_plug(&plug);
-	while ((folio = writeback_iter(mapping, wbc, folio, &err))) {
-		err = mapping->a_ops->writepage(&folio->page, wbc);
-		if (err == AOP_WRITEPAGE_ACTIVATE) {
-			folio_unlock(folio);
-			err = 0;
-		}
-		mapping_set_error(mapping, err);
-	}
-	blk_finish_plug(&plug);
-
-	return err;
-}
-
 int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
 {
 	int ret;
@@ -2652,14 +2631,11 @@ int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
 	wb = inode_to_wb_wbc(mapping->host, wbc);
 	wb_bandwidth_estimate_start(wb);
 	while (1) {
-		if (mapping->a_ops->writepages) {
+		if (mapping->a_ops->writepages)
 			ret = mapping->a_ops->writepages(mapping, wbc);
-		} else if (mapping->a_ops->writepage) {
-			ret = writeback_use_writepage(mapping, wbc);
-		} else {
+		else
 			/* deal with chardevs and other special files */
 			ret = 0;
-		}
 		if (ret != -ENOMEM || wbc->sync_mode != WB_SYNC_ALL)
 			break;