Commit 5d87c7fc authored Jan 05, 2026 by Zhang Yi Committed by Theodore Ts'o Jan 19, 2026

ext4: avoid starting handle when dio writing an unwritten extent



Since we have deferred the split of the unwritten extent until after I/O
completion, it is not necessary to initiate the journal handle when
submitting the I/O.

This can improve the write performance of concurrent DIO for multiple
files. The fio tests below show a ~25% performance improvement when
wirting to unwritten files on my VM with a mem disk.

  [unwritten]
  direct=1
  ioengine=psync
  numjobs=16
  rw=write     # write/randwrite
  bs=4K
  iodepth=1
  directory=/mnt
  size=5G
  runtime=30s
  overwrite=0
  norandommap=1
  fallocate=native
  ramp_time=5s
  group_reporting=1

 [w/o]
  w:  IOPS=62.5k, BW=244MiB/s
  rw: IOPS=56.7k, BW=221MiB/s

 [w]
  w:  IOPS=79.6k, BW=311MiB/s
  rw: IOPS=70.2k, BW=274MiB/s

Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Link: https://patch.msgid.link/20260105014522.1937690-4-yi.zhang@huaweicloud.com


Signed-off-by: Theodore Ts'o <tytso@mit.edu>

parent ea96cb5c

fs/ext4/file.c

+1 −3

Original line number	Diff line number	Diff line
		@@ -418,9 +418,7 @@ static const struct iomap_dio_ops ext4_dio_write_ops = {
		* updating inode i_disksize and/or orphan handling with exclusive lock.
		*
		* - shared locking will only be true mostly with overwrites, including
		* initialized blocks and unwritten blocks. For overwrite unwritten blocks
		* we protect splitting extents by i_data_sem in ext4_inode_info, so we can
		* also release exclusive i_rwsem lock.
		* initialized blocks and unwritten blocks.
		*
		* - Otherwise we will switch to exclusive i_rwsem lock.
		*/

fs/ext4/inode.c

+7 −2

Original line number	Diff line number	Diff line
		@@ -3813,9 +3813,14 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
		ret = ext4_map_blocks(NULL, inode, &map, 0);
		/*
		* For atomic writes the entire requested length should
		* be mapped.
		*/
		if (map.m_flags & EXT4_MAP_MAPPED) {
		* be mapped. For DAX we convert extents to initialized
		* ones before copying the data, otherwise we do it
		* after I/O so there's no need to call into
		* ext4_iomap_alloc().
		*/
		if ((map.m_flags & EXT4_MAP_MAPPED) \|\|
		(!(flags & IOMAP_DAX) &&
		(map.m_flags & EXT4_MAP_UNWRITTEN))) {
		if ((!(flags & IOMAP_ATOMIC) && ret > 0) \|\|
		(flags & IOMAP_ATOMIC && ret >= orig_mlen))
		goto out;