linux-kernel - [PATCH 10/16] blk-mq-sched: unify elevators checking for async requests

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Message-Id: <20250814033522.770575-11-yukuai1@huaweicloud.com>
Date: Thu, 14 Aug 2025 11:35:16 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: axboe@...nel.dk,
	yukuai3@...wei.com,
	bvanassche@....org,
	nilay@...ux.ibm.com,
	hare@...e.de,
	ming.lei@...hat.com
Cc: linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	yukuai1@...weicloud.com,
	yi.zhang@...wei.com,
	yangerkun@...wei.com,
	johnny.chenyi@...wei.com
Subject: [PATCH 10/16] blk-mq-sched: unify elevators checking for async requests

From: Yu Kuai <yukuai3@...wei.com>

bfq and mq-deadline consider sync writes as async requests and only
resver tags for sync reads by async_depth, however, kyber doesn't
consider sync writes as async requests.

Consider the case there are lots of dirty pages, and user do fsync,
in this case sched_tags can be exhausted by sync writes and sync reads
can stuck waiting for tag. Hence let kyber follow what mq-deadline and
bfq did, and unify async requests checking for all elevators.

Signed-off-by: Yu Kuai <yukuai3@...wei.com>
---
 block/bfq-iosched.c   | 2 +-
 block/blk-mq-sched.h  | 5 +++++
 block/kyber-iosched.c | 2 +-
 block/mq-deadline.c   | 2 +-
 4 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index c0c398998aa1..de0dee255ccf 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -697,7 +697,7 @@ static void bfq_limit_depth(blk_opf_t opf, struct blk_mq_alloc_data *data)
 	unsigned int limit, act_idx;
 
 	/* Sync reads have full depth available */
-	if (op_is_sync(opf) && !op_is_write(opf))
+	if (blk_mq_sched_sync_request(opf))
 		limit = data->q->nr_requests;
 	else
 		limit = bfqd->async_depths[!!bfqd->wr_busy_queues][op_is_sync(opf)];
diff --git a/block/blk-mq-sched.h b/block/blk-mq-sched.h
index 8e21a6b1415d..ae747f9053c7 100644
--- a/block/blk-mq-sched.h
+++ b/block/blk-mq-sched.h
@@ -103,4 +103,9 @@ static inline void blk_mq_set_min_shallow_depth(struct request_queue *q,
 						depth);
 }
 
+static inline bool blk_mq_sched_sync_request(blk_opf_t opf)
+{
+	return op_is_sync(opf) && !op_is_write(opf);
+}
+
 #endif
diff --git a/block/kyber-iosched.c b/block/kyber-iosched.c
index 49ae52aa20d9..b3df807044c3 100644
--- a/block/kyber-iosched.c
+++ b/block/kyber-iosched.c
@@ -543,7 +543,7 @@ static void kyber_limit_depth(blk_opf_t opf, struct blk_mq_alloc_data *data)
 	 * We use the scheduler tags as per-hardware queue queueing tokens.
 	 * Async requests can be limited at this stage.
 	 */
-	if (!op_is_sync(opf)) {
+	if (!blk_mq_sched_sync_request(opf)) {
 		struct kyber_queue_data *kqd = data->q->elevator->elevator_data;
 
 		data->shallow_depth = kqd->async_depth;
diff --git a/block/mq-deadline.c b/block/mq-deadline.c
index 578bc79c5654..1825173d82a6 100644
--- a/block/mq-deadline.c
+++ b/block/mq-deadline.c
@@ -496,7 +496,7 @@ static void dd_limit_depth(blk_opf_t opf, struct blk_mq_alloc_data *data)
 	struct deadline_data *dd = data->q->elevator->elevator_data;
 
 	/* Do not throttle synchronous reads. */
-	if (op_is_sync(opf) && !op_is_write(opf))
+	if (blk_mq_sched_sync_request(opf))
 		return;
 
 	/*
-- 
2.39.2