The following code paths may result in high latency or even task hangs:
1. fastcommit io is throttled by wbt.
2. jbd2_fc_wait_bufs() might wait for a long time while
JBD2_FAST_COMMIT_ONGOING is set in journal->flags, and then
jbd2_journal_commit_transaction() waits for the
JBD2_FAST_COMMIT_ONGOING bit for a long time while holding the write
lock of j_state_lock.
3. start_this_handle() waits for read lock of j_state_lock which
results in high latency or task hang.
Given the fact that ext4_fc_commit() already modifies the current
process' IO priority to match that of the jbd2 thread, it should be
reasonable to match jbd2's IO submission flags as well.
Suggested-by: Ritesh Harjani (IBM) <ritesh.list@xxxxxxxxx>
Signed-off-by: Julian Sun <sunjunchao@xxxxxxxxxxxxx>
---
fs/ext4/fast_commit.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/ext4/fast_commit.c b/fs/ext4/fast_commit.c
index 42bee1d4f9f9..fa66b08de999 100644
--- a/fs/ext4/fast_commit.c
+++ b/fs/ext4/fast_commit.c
@@ -663,7 +663,7 @@ void ext4_fc_track_range(handle_t *handle, struct inode *inode, ext4_lblk_t star
static void ext4_fc_submit_bh(struct super_block *sb, bool is_tail)
{
- blk_opf_t write_flags = REQ_SYNC;
+ blk_opf_t write_flags = JBD2_JOURNAL_REQ_FLAGS;
struct buffer_head *bh = EXT4_SB(sb)->s_fc_bh;
/* Add REQ_FUA | REQ_PREFLUSH only its tail */
--
2.20.1
