blk-ioprio: Remove unneeded field

blkcg->ioprio_set field is not really useful except for avoiding
possibly more expensive checks inside blkcg_ioprio_track(). The check
for blkcg->prio_policy being equal to POLICY_NO_CHANGE does the same
service so just remove the ioprio_set field and replace the check.

Reviewed-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Tested-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20220623074840.5960-6-jack@suse.cz
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-ioprio.c

@@ -62,7 +62,6 @@ struct ioprio_blkg {
 struct ioprio_blkcg {
 	struct blkcg_policy_data cpd;
 	enum prio_policy	 prio_policy;
-	bool			 prio_set;
 };
 
 static inline struct ioprio_blkg *pd_to_ioprio(struct blkg_policy_data *pd)
@@ -113,7 +112,6 @@ static ssize_t ioprio_set_prio_policy(struct kernfs_open_file *of, char *buf,
 	if (ret < 0)
 		return ret;
 	blkcg->prio_policy = ret;
-	blkcg->prio_set = true;
 	return nbytes;
 }
 
@@ -193,16 +191,15 @@ static void blkcg_ioprio_track(struct rq_qos *rqos, struct request *rq,
 	struct ioprio_blkcg *blkcg = ioprio_blkcg_from_bio(bio);
 	u16 prio;
 
-	if (!blkcg->prio_set)
+	if (blkcg->prio_policy == POLICY_NO_CHANGE)
 		return;
 
 	/*
 	 * Except for IOPRIO_CLASS_NONE, higher I/O priority numbers
 	 * correspond to a lower priority. Hence, the max_t() below selects
 	 * the lower priority of bi_ioprio and the cgroup I/O priority class.
-	 * If the cgroup policy has been set to POLICY_NO_CHANGE == 0, the
-	 * bio I/O priority is not modified. If the bio I/O priority equals
-	 * IOPRIO_CLASS_NONE, the cgroup I/O priority is assigned to the bio.
+	 * If the bio I/O priority equals IOPRIO_CLASS_NONE, the cgroup I/O
+	 * priority is assigned to the bio.
 	 */
 	prio = max_t(u16, bio->bi_ioprio,
 			IOPRIO_PRIO_VALUE(blkcg->prio_policy, 0));