When a bio with REQ_PREFLUSH is submitted to dm, __send_empty_flush()
generates a flush_bio with REQ_OP_WRITE | REQ_PREFLUSH | REQ_SYNC,
which causes the flush_bio to be throttled by wbt_wait().
An example from v5.4, similar problem also exists in upstream:
crash> bt 2091206
PID: 2091206 TASK: ffff2050df92a300 CPU: 109 COMMAND: "kworker/u260:0"
#0 [ffff800084a2f7f0] __switch_to at ffff80004008aeb8
#1 [ffff800084a2f820] __schedule at ffff800040bfa0c4
#2 [ffff800084a2f880] schedule at ffff800040bfa4b4
#3 [ffff800084a2f8a0] io_schedule at ffff800040bfa9c4
#4 [ffff800084a2f8c0] rq_qos_wait at ffff8000405925bc
#5 [ffff800084a2f940] wbt_wait at ffff8000405bb3a0
#6 [ffff800084a2f9a0] __rq_qos_throttle at ffff800040592254
#7 [ffff800084a2f9c0] blk_mq_make_request at ffff80004057cf38
#8 [ffff800084a2fa60] generic_make_request at ffff800040570138
#9 [ffff800084a2fae0] submit_bio at ffff8000405703b4
#10 [ffff800084a2fb50] xlog_write_iclog at ffff800001280834 [xfs]
#11 [ffff800084a2fbb0] xlog_sync at ffff800001280c3c [xfs]
#12 [ffff800084a2fbf0] xlog_state_release_iclog at ffff800001280df4 [xfs]
#13 [ffff800084a2fc10] xlog_write at ffff80000128203c [xfs]
#14 [ffff800084a2fcd0] xlog_cil_push at ffff8000012846dc [xfs]
#15 [ffff800084a2fda0] xlog_cil_push_work at ffff800001284a2c [xfs]
#16 [ffff800084a2fdb0] process_one_work at ffff800040111d08
#17 [ffff800084a2fe00] worker_thread at ffff8000401121cc
#18 [ffff800084a2fe70] kthread at ffff800040118de4
After commit 2def2845cc33 ("xfs: don't allow log IO to be throttled"),
the metadata submitted by xlog_write_iclog() should not be throttled.
But due to the existence of the dm layer, throttling flush_bio indirectly
causes the metadata bio to be throttled.
Fix this by conditionally adding REQ_IDLE to flush_bio.bi_opf, which makes
wbt_should_throttle() return false to avoid wbt_wait().
Signed-off-by: Jinliang Zheng <alexjlzheng@xxxxxxxxxxx>
Reviewed-by: Tianxiang Peng <txpeng@xxxxxxxxxxx>
Reviewed-by: Hao Peng <flyingpeng@xxxxxxxxxxx>
---
drivers/md/dm.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 4d1e42891d24..5ab7574c0c76 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1540,14 +1540,18 @@ static void __send_empty_flush(struct clone_info *ci)
{
struct dm_table *t = ci->map;
struct bio flush_bio;
+ blk_opf_t opf = REQ_OP_WRITE | REQ_PREFLUSH | REQ_SYNC;
+
+ if ((ci->io->orig_bio->bi_opf & (REQ_IDLE | REQ_SYNC)) ==
+ (REQ_IDLE | REQ_SYNC))
+ opf |= REQ_IDLE;
/*
* Use an on-stack bio for this, it's safe since we don't
* need to reference it after submit. It's just used as
* the basis for the clone(s).
*/
- bio_init(&flush_bio, ci->io->md->disk->part0, NULL, 0,
- REQ_OP_WRITE | REQ_PREFLUSH | REQ_SYNC);
+ bio_init(&flush_bio, ci->io->md->disk->part0, NULL, 0, opf);
ci->bio = &flush_bio;
ci->sector_count = 0;
--
2.41.1
