minix: don't flush page immediately for DIRSYNC directories

We do not need to writeout modified directory blocks immediately when
modifying them while the page is locked. It is enough to do the flush
somewhat later which has the added benefit that inode times can be
flushed as well. It also allows us to stop depending on
write_one_page() function.

Ported from an ext2 patch by Jan Kara.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/minix/dir.c

@@ -46,21 +46,27 @@ minix_last_byte(struct inode *inode, unsigned long page_nr)
 	return last_byte;
 }
 
-static int dir_commit_chunk(struct page *page, loff_t pos, unsigned len)
+static void dir_commit_chunk(struct page *page, loff_t pos, unsigned len)
 {
 	struct address_space *mapping = page->mapping;
 	struct inode *dir = mapping->host;
-	int err = 0;
+
 	block_write_end(NULL, mapping, pos, len, len, page, NULL);
 
 	if (pos+len > dir->i_size) {
 		i_size_write(dir, pos+len);
 		mark_inode_dirty(dir);
 	}
-	if (IS_DIRSYNC(dir))
-		err = write_one_page(page);
-	else
-		unlock_page(page);
+	unlock_page(page);
+}
+
+static int minix_handle_dirsync(struct inode *dir)
+{
+	int err;
+
+	err = filemap_write_and_wait(dir->i_mapping);
+	if (!err)
+		err = sync_inode_metadata(dir, 1);
 	return err;
 }
 
@@ -274,9 +280,10 @@ int minix_add_link(struct dentry *dentry, struct inode *inode)
 		memset (namx + namelen, 0, sbi->s_dirsize - namelen - 2);
 		de->inode = inode->i_ino;
 	}
-	err = dir_commit_chunk(page, pos, sbi->s_dirsize);
+	dir_commit_chunk(page, pos, sbi->s_dirsize);
 	dir->i_mtime = dir->i_ctime = current_time(dir);
 	mark_inode_dirty(dir);
+	err = minix_handle_dirsync(dir);
 out_put:
 	dir_put_page(page);
 out:
@@ -305,12 +312,10 @@ int minix_delete_entry(struct minix_dir_entry *de, struct page *page)
 		((minix3_dirent *)de)->inode = 0;
 	else
 		de->inode = 0;
-	err = dir_commit_chunk(page, pos, len);
-	if (err)
-		return err;
+	dir_commit_chunk(page, pos, len);
 	inode->i_ctime = inode->i_mtime = current_time(inode);
 	mark_inode_dirty(inode);
-	return 0;
+	return minix_handle_dirsync(inode);
 }
 
 int minix_make_empty(struct inode *inode, struct inode *dir)
@@ -350,7 +355,8 @@ int minix_make_empty(struct inode *inode, struct inode *dir)
 	}
 	kunmap_atomic(kaddr);
 
-	err = dir_commit_chunk(page, 0, 2 * sbi->s_dirsize);
+	dir_commit_chunk(page, 0, 2 * sbi->s_dirsize);
+	err = minix_handle_dirsync(inode);
 fail:
 	put_page(page);
 	return err;
@@ -429,12 +435,10 @@ int minix_set_link(struct minix_dir_entry *de, struct page *page,
 		((minix3_dirent *)de)->inode = inode->i_ino;
 	else
 		de->inode = inode->i_ino;
-	err = dir_commit_chunk(page, pos, sbi->s_dirsize);
-	if (err)
-		return err;
+	dir_commit_chunk(page, pos, sbi->s_dirsize);
 	dir->i_mtime = dir->i_ctime = current_time(dir);
 	mark_inode_dirty(dir);
-	return 0;
+	return minix_handle_dirsync(dir);
 }
 
 struct minix_dir_entry * minix_dotdot (struct inode *dir, struct page **p)