udf: add writepages support for udf

Use mpage_writepages() instead of multiple calls to udf_writepage()
to make performance higher.

*Write Speed with writepage() =
 RecSize     ReadSpeed    WriteSpeed  RanReadSpeed RanWriteSpeed
10485760    0.00MB/sec    8.56MB/sec    0.00MB/sec    8.20MB/sec
 1048576    0.00MB/sec    8.57MB/sec    0.00MB/sec    6.42MB/sec
  524288    0.00MB/sec    8.59MB/sec    0.00MB/sec    5.24MB/sec
  262144    0.00MB/sec    8.59MB/sec    0.00MB/sec    4.17MB/sec
  131072    0.00MB/sec    8.53MB/sec    0.00MB/sec    3.32MB/sec
   65536    0.00MB/sec    8.49MB/sec    0.00MB/sec    2.31MB/sec

*Write Speed with writepages()
RecSize     ReadSpeed    WriteSpeed  RanReadSpeed RanWriteSpeed
10485760    0.00MB/sec    9.88MB/sec    0.00MB/sec    9.60MB/sec
 1048576    0.00MB/sec    9.95MB/sec    0.00MB/sec    7.52MB/sec
  524288    0.00MB/sec    9.98MB/sec    0.00MB/sec    6.16MB/sec
  262144    0.00MB/sec    9.90MB/sec    0.00MB/sec    4.98MB/sec
  131072    0.00MB/sec    9.89MB/sec    0.00MB/sec    3.78MB/sec
   65536    0.00MB/sec    9.81MB/sec    0.00MB/sec    2.50MB/sec

There is about 1.4MB/sec speed improvement over 8.5MB/sec,
which comes out around 16% improvement.
Signed-off-by: Namjae Jeon <linkinjeon@gmail.com>
Signed-off-by: Ashish Sangwan <ashish.sangwan2@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>

fs/udf/inode.c

@@ -100,6 +100,12 @@ static int udf_writepage(struct page *page, struct writeback_control *wbc)
 	return block_write_full_page(page, udf_get_block, wbc);
 }
 
+static int udf_writepages(struct address_space *mapping,
+			struct writeback_control *wbc)
+{
+	return mpage_writepages(mapping, wbc, udf_get_block);
+}
+
 static int udf_readpage(struct file *file, struct page *page)
 {
 	return mpage_readpage(page, udf_get_block);
@@ -145,6 +151,7 @@ const struct address_space_operations udf_aops = {
 	.readpage	= udf_readpage,
 	.readpages	= udf_readpages,
 	.writepage	= udf_writepage,
+	.writepages	= udf_writepages,
 	.write_begin		= udf_write_begin,
 	.write_end		= generic_write_end,
 	.bmap		= udf_bmap,