[PATCH v2 1/7] block: fix plug list flushing for nomerge queues

[Ming Lei <ming.lei@canonical.com>]

From: Jeff Moyer <jmoyer@redhat.com>

Request queues with merging disabled will not flush the plug list after
BLK_MAX_REQUEST_COUNT requests have been queued, since the code relies
on blk_attempt_plug_merge to compute the request_count.  Fix this by
computing the number of queued requests even for nomerge queues.

Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
---
 block/blk-core.c | 32 +++++++++++++++++++++++++++++---
 block/blk-mq.c   |  9 ++++++---
 block/blk.h      |  1 +
 3 files changed, 36 insertions(+), 6 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 0391206..4a45d00 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1594,6 +1594,30 @@ out:
 	return ret;
 }
 
+unsigned int blk_plug_queued_count(struct request_queue *q)
+{
+	struct blk_plug *plug;
+	struct request *rq;
+	struct list_head *plug_list;
+	unsigned int ret = 0;
+
+	plug = current->plug;
+	if (!plug)
+		goto out;
+
+	if (q->mq_ops)
+		plug_list = &plug->mq_list;
+	else
+		plug_list = &plug->list;
+
+	list_for_each_entry(rq, plug_list, queuelist) {
+		if (rq->q == q)
+			ret++;
+	}
+out:
+	return ret;
+}
+
 void init_request_from_bio(struct request *req, struct bio *bio)
 {
 	req->cmd_type = REQ_TYPE_FS;
@@ -1641,9 +1665,11 @@ static void blk_queue_bio(struct request_queue *q, struct bio *bio)
 	 * Check if we can merge with the plugged list before grabbing
 	 * any locks.
 	 */
-	if (!blk_queue_nomerges(q) &&
-	    blk_attempt_plug_merge(q, bio, &request_count, NULL))
-		return;
+	if (!blk_queue_nomerges(q)) {
+		if (blk_attempt_plug_merge(q, bio, &request_count, NULL))
+			return;
+	} else
+		request_count = blk_plug_queued_count(q);
 
 	spin_lock_irq(q->queue_lock);
 
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 546b3b8..1796b31 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1268,9 +1268,12 @@ static void blk_mq_make_request(struct request_queue *q, struct bio *bio)
 
 	blk_queue_split(q, &bio, q->bio_split);
 
-	if (!is_flush_fua && !blk_queue_nomerges(q) &&
-	    blk_attempt_plug_merge(q, bio, &request_count, &same_queue_rq))
-		return;
+	if (!is_flush_fua && !blk_queue_nomerges(q)) {
+		if (blk_attempt_plug_merge(q, bio, &request_count,
+					   &same_queue_rq))
+			return;
+	} else
+		request_count = blk_plug_queued_count(q);
 
 	rq = blk_mq_map_request(q, bio, &data);
 	if (unlikely(!rq))
diff --git a/block/blk.h b/block/blk.h
index 98614ad..aa27d02 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -86,6 +86,7 @@ bool bio_attempt_back_merge(struct request_queue *q, struct request *req,
 bool blk_attempt_plug_merge(struct request_queue *q, struct bio *bio,
 			    unsigned int *request_count,
 			    struct request **same_queue_rq);
+unsigned int blk_plug_queued_count(struct request_queue *q);
 
 void blk_account_io_start(struct request *req, bool new_io);
 void blk_account_io_completion(struct request *req, unsigned int bytes);
-- 
1.9.1