ext4: Convert ext4_write_end() to use a folio

Convert the incoming struct page to a folio.  Replaces two implicit
calls to compound_head() with one explicit call.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Link: https://lore.kernel.org/r/20230324180129.1220691-18-willy@infradead.org
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/inode.c

@@ -1289,6 +1289,7 @@ static int ext4_write_end(struct file *file,
 			  loff_t pos, unsigned len, unsigned copied,
 			  struct page *page, void *fsdata)
 {
+	struct folio *folio = page_folio(page);
 	handle_t *handle = ext4_journal_current_handle();
 	struct inode *inode = mapping->host;
 	loff_t old_size = inode->i_size;
@@ -1304,7 +1305,7 @@ static int ext4_write_end(struct file *file,
 
 	copied = block_write_end(file, mapping, pos, len, copied, page, fsdata);
 	/*
-	 * it's important to update i_size while still holding page lock:
+	 * it's important to update i_size while still holding folio lock:
 	 * page writeout could otherwise come in and zero beyond i_size.
 	 *
 	 * If FS_IOC_ENABLE_VERITY is running on this inode, then Merkle tree
@@ -1312,15 +1313,15 @@ static int ext4_write_end(struct file *file,
 	 */
 	if (!verity)
 		i_size_changed = ext4_update_inode_size(inode, pos + copied);
-	unlock_page(page);
-	put_page(page);
+	folio_unlock(folio);
+	folio_put(folio);
 
 	if (old_size < pos && !verity)
 		pagecache_isize_extended(inode, old_size, pos);
 	/*
-	 * Don't mark the inode dirty under page lock. First, it unnecessarily
-	 * makes the holding time of page lock longer. Second, it forces lock
-	 * ordering of page lock and transaction start for journaling
+	 * Don't mark the inode dirty under folio lock. First, it unnecessarily
+	 * makes the holding time of folio lock longer. Second, it forces lock
+	 * ordering of folio lock and transaction start for journaling
 	 * filesystems.
 	 */
 	if (i_size_changed)