nilfs2: remove nilfs_writepage

Since nilfs2 has a ->writepages operation already, ->writepage is only
called by the migration code.  If we add a ->migrate_folio operation, it
won't even be used for that and so it can be deleted.

[konishi.ryusuke@gmail.com: fixed panic by using buffer_migrate_folio_norefs]
Link: https://lkml.kernel.org/r/20241002150036.1339475-2-willy@infradead.org
Link: https://lkml.kernel.org/r/20241024092602.13395-10-konishi.ryusuke@gmail.com
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: Matthew Wilcox (Oracle)

fs/nilfs2/inode.c

@@ -170,37 +170,6 @@ static int nilfs_writepages(struct address_space *mapping,
 	return err;
 }
 
-static int nilfs_writepage(struct page *page, struct writeback_control *wbc)
-{
-	struct folio *folio = page_folio(page);
-	struct inode *inode = folio->mapping->host;
-	int err;
-
-	if (sb_rdonly(inode->i_sb)) {
-		/*
-		 * It means that filesystem was remounted in read-only
-		 * mode because of error or metadata corruption. But we
-		 * have dirty pages that try to be flushed in background.
-		 * So, here we simply discard this dirty page.
-		 */
-		nilfs_clear_folio_dirty(folio);
-		folio_unlock(folio);
-		return -EROFS;
-	}
-
-	folio_redirty_for_writepage(wbc, folio);
-	folio_unlock(folio);
-
-	if (wbc->sync_mode == WB_SYNC_ALL) {
-		err = nilfs_construct_segment(inode->i_sb);
-		if (unlikely(err))
-			return err;
-	} else if (wbc->for_reclaim)
-		nilfs_flush_segment(inode->i_sb, inode->i_ino);
-
-	return 0;
-}
-
 static bool nilfs_dirty_folio(struct address_space *mapping,
 		struct folio *folio)
 {
@@ -295,7 +264,6 @@ nilfs_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
 }
 
 const struct address_space_operations nilfs_aops = {
-	.writepage		= nilfs_writepage,
 	.read_folio		= nilfs_read_folio,
 	.writepages		= nilfs_writepages,
 	.dirty_folio		= nilfs_dirty_folio,
@@ -304,6 +272,7 @@ const struct address_space_operations nilfs_aops = {
 	.write_end		= nilfs_write_end,
 	.invalidate_folio	= block_invalidate_folio,
 	.direct_IO		= nilfs_direct_IO,
+	.migrate_folio		= buffer_migrate_folio_norefs,
 	.is_partially_uptodate  = block_is_partially_uptodate,
 };