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) Signed-off-by: Julian Sun --- 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