[PATCH RFC 2/2] ext4: Optimize endio process for DIO overwrites

[Zhihao Cheng]

In DIO overwriting case, there is no need to convert unwritten exntents
and ext4_handle_inode_extension() can be ignored, which means that endio
process can be executed under irq context. Since commit 240930fb7e6b5
("ext4: dio take shared inode lock when overwriting preallocated blocks")
has provided a method to judge whether overwriting is happening, just do
nothing in endio process if DIO overwriting happens.
This patch enables ext4 processing endio under irq context in DIO
overwriting case, which brings a performance improvement in the
following fio test on a x86 physical machine with nvme when irq
and fio run on the same cpu:

Test: fio -direct=1 -iodepth=128 -rw=randwrite -ioengine=libaio -bs=4k
-size=2G -numjobs=1 -overwrite=1 -time_based -runtime=60 -group_reporting
-filename=/test/test -name=Rand_write_Testing --cpus_allowed=1

before: 953 MiB/s  after: 1350 MiB/s, ~41% perf improvement.

Suggested-by: Zhang Yi <yi.zhang@xxxxxxxxxx>
Signed-off-by: Zhihao Cheng <chengzhihao1@xxxxxxxxxx>
---
 fs/ext4/file.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index 54d6ff22585c..411a05c6b96e 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -503,6 +503,7 @@ static ssize_t ext4_dio_write_iter(struct kiocb *iocb, struct iov_iter *from)
 	loff_t offset = iocb->ki_pos;
 	size_t count = iov_iter_count(from);
 	const struct iomap_ops *iomap_ops = &ext4_iomap_ops;
+	const struct iomap_dio_ops *iomap_dops = &ext4_dio_write_ops;
 	bool extend = false, unwritten = false;
 	bool ilock_shared = true;
 	int dio_flags = 0;
@@ -572,9 +573,12 @@ static ssize_t ext4_dio_write_iter(struct kiocb *iocb, struct iov_iter *from)
 		ext4_journal_stop(handle);
 	}
 
-	if (ilock_shared && !unwritten)
+	if (ilock_shared && !unwritten) {
 		iomap_ops = &ext4_iomap_overwrite_ops;
-	ret = iomap_dio_rw(iocb, from, iomap_ops, &ext4_dio_write_ops,
+		iomap_dops = NULL;
+		dio_flags = IOMAP_DIO_MAY_INLINE_COMP;
+	}
+	ret = iomap_dio_rw(iocb, from, iomap_ops, iomap_dops,
 			   dio_flags, NULL, 0);
 	if (ret == -ENOTBLK)
 		ret = 0;
-- 
2.39.2