在 2025/8/27 04:55, Ritesh Harjani (IBM) 写道:
Julian Sun <sunjunchao@xxxxxxxxxxxxx> writes:
In commit 6a3afb6ac6df ("jbd2: increase the journal IO's priority"),
the priority of IOs initiated by jbd2 has been raised, exempting them
from WBT throttling.
Checkpoint is also a crucial operation of jbd2. While no serious issues
have been observed so far, it should still be reasonable to exempt
checkpoint from WBT throttling.
Interesting.. I was wondering whether we were able to observe any
throttling for jbd2 log writes or for jbd2 checkpoint?
Maybe It would have been nice, if we had some kind of data for this.
Good idea. But AFAICS wbt lacks of such a obversation mechanism now..>
BTW - does it make sense for fastcommit path too maybe for non-tail
fc write requests? I think it uses ext4_fc_submit_bh().
Yeah, I think so.
After a rough check of the code, the following code paths may result in
high latency or even task hangs:
1. fastcommit io is throttled by wbt or other block layer qos policies.
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.
Hi, Jan, please correct me if I'm missing anything.
-ritesh
Signed-off-by: Julian Sun <sunjunchao@xxxxxxxxxxxxx>
---
fs/jbd2/checkpoint.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/jbd2/checkpoint.c b/fs/jbd2/checkpoint.c
index 38861ca04899..2d0719bf6d87 100644
--- a/fs/jbd2/checkpoint.c
+++ b/fs/jbd2/checkpoint.c
@@ -131,7 +131,7 @@ __flush_batch(journal_t *journal, int *batch_count)
blk_start_plug(&plug);
for (i = 0; i < *batch_count; i++)
- write_dirty_buffer(journal->j_chkpt_bhs[i], REQ_SYNC);
+ write_dirty_buffer(journal->j_chkpt_bhs[i], JBD2_JOURNAL_REQ_FLAGS);
blk_finish_plug(&plug);
for (i = 0; i < *batch_count; i++) {
--
2.20.1
Thanks,
--
Julian Sun <sunjunchao@xxxxxxxxxxxxx>
