[PATCH v2 2/4] blk-flush: count inflight flush_data requests

chengming.zhou
2023-06-29T11:07:58Z

From: Chengming Zhou <zhouchengming@bytedance.com>

The flush state machine use a double list to link all inflight
flush_data requests, to avoid issuing separate post-flushes for
these flush_data requests which shared PREFLUSH.

So we can't reuse rq->queuelist, this is why we need rq->flush.list

In preparation of the next patch that reuse rq->queuelist for flush
state machine, we change the double linked list to unsigned long
counter, which count all inflight flush_data requests.

This is ok since we only need to know if there is any inflight
flush_data request, so unsigned long counter is good.

Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
---
block/blk-flush.c | 9 +++++----
block/blk.h | 5 ++---
2 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/block/blk-flush.c b/block/blk-flush.c
index dba392cf22be..bb7adfc2a5da 100644
--- a/block/blk-flush.c
+++ b/block/blk-flush.c
@@ -187,7 +187,8 @@ static void blk_flush_complete_seq(struct request *rq,
break;

case REQ_FSEQ_DATA:
- list_move_tail(&rq->flush.list, &fq->flush_data_in_flight);
+ list_del_init(&rq->flush.list);
+ fq->flush_data_in_flight++;
spin_lock(&q->requeue_lock);
list_add_tail(&rq->queuelist, &q->flush_list);
spin_unlock(&q->requeue_lock);
@@ -299,7 +300,7 @@ static void blk_kick_flush(struct request_queue *q, struct blk_flush_queue *fq,
return;

/* C2 and C3 */
- if (!list_empty(&fq->flush_data_in_flight) &&
+ if (fq->flush_data_in_flight &&
time_before(jiffies,
fq->flush_pending_since + FLUSH_PENDING_TIMEOUT))
return;
@@ -374,6 +375,7 @@ static enum rq_end_io_ret mq_flush_data_end_io(struct request *rq,
* the comment in flush_end_io().
*/
spin_lock_irqsave(&fq->mq_flush_lock, flags);
+ fq->flush_data_in_flight--;
blk_flush_complete_seq(rq, fq, REQ_FSEQ_DATA, error);
spin_unlock_irqrestore(&fq->mq_flush_lock, flags);

@@ -445,7 +447,7 @@ bool blk_insert_flush(struct request *rq)
blk_rq_init_flush(rq);
rq->flush.seq |= REQ_FSEQ_POSTFLUSH;
spin_lock_irq(&fq->mq_flush_lock);
- list_move_tail(&rq->flush.list, &fq->flush_data_in_flight);
+ fq->flush_data_in_flight++;
spin_unlock_irq(&fq->mq_flush_lock);
return false;
default:
@@ -496,7 +498,6 @@ struct blk_flush_queue *blk_alloc_flush_queue(int node, int cmd_size,

INIT_LIST_HEAD(&fq->flush_queue[0]);
INIT_LIST_HEAD(&fq->flush_queue[1]);
- INIT_LIST_HEAD(&fq->flush_data_in_flight);

return fq;

diff --git a/block/blk.h b/block/blk.h
index 608c5dcc516b..686712e13835 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -15,15 +15,14 @@ struct elevator_type;
extern struct dentry *blk_debugfs_root;

struct blk_flush_queue {
+ spinlock_t mq_flush_lock;
unsigned int flush_pending_idx:1;
unsigned int flush_running_idx:1;
blk_status_t rq_status;
unsigned long flush_pending_since;
struct list_head flush_queue[2];
- struct list_head flush_data_in_flight;
+ unsigned long flush_data_in_flight;
struct request *flush_rq;
-
- spinlock_t mq_flush_lock;
};

bool is_flush_rq(struct request *req);
--
2.39.2