[PATCH v2 4/4] blk-flush: don't need to end rq twice for non postflush

[chengming.zhou@linux.dev]

From: Chengming Zhou <zhouchengming@bytedance.com>

Now we unconditionally blk_rq_init_flush() to replace rq->end_io to
make rq return twice back to the flush state machine for post-flush.

Obviously, non post-flush requests don't need it, they don't need to
end request twice, so they don't need to replace rq->end_io callback.
And the same for requests with the FUA bit on hardware with FUA support.

There are also some other good points:
1. all requests on hardware with FUA support won't have post-flush, so
   all of them don't need to end twice.

2. non post-flush requests won't have RQF_FLUSH_SEQ rq_flags set, so
   they can merge like normal requests.

3. we don't account non post-flush requests in flush_data_in_flight,
   since there is no point to defer pending flush for these requests.

Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
---
 block/blk-flush.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/block/blk-flush.c b/block/blk-flush.c
index ed195c760617..a299dae65350 100644
--- a/block/blk-flush.c
+++ b/block/blk-flush.c
@@ -178,7 +178,8 @@ static void blk_end_flush(struct request *rq, struct blk_flush_queue *fq,
 	 * normal completion and end it.
 	 */
 	list_del_init(&rq->queuelist);
-	blk_flush_restore_request(rq);
+	if (rq->rq_flags & RQF_FLUSH_SEQ)
+		blk_flush_restore_request(rq);
 	blk_mq_end_request(rq, error);
 
 	blk_kick_flush(q, fq);
@@ -461,7 +462,8 @@ bool blk_insert_flush(struct request *rq)
 		 * Mark the request as part of a flush sequence and submit it
 		 * for further processing to the flush state machine.
 		 */
-		blk_rq_init_flush(rq);
+		if (policy & REQ_FSEQ_POSTFLUSH)
+			blk_rq_init_flush(rq);
 		spin_lock_irq(&fq->mq_flush_lock);
 		blk_enqueue_preflush(rq, fq);
 		spin_unlock_irq(&fq->mq_flush_lock);
-- 
2.41.0