[PATCH RFC -next 6/7] blk-iocost: support to free iocost

[Yu Kuai <yukuai1@xxxxxxxxxxxxxxx>]

From: Yu Kuai <yukuai3@xxxxxxxxxx>

Currently if iocost is initialized, it can never be freed until the disk
is deleted.

A new param "free" is added to the blk-io cgroup api "io.cost.qos", and
user can use it to free iocost. On the one hand prevent overhead from
fast path, on the other hand prepare to build iocost as kernel module.

Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
---
 block/blk-iocost.c | 38 +++++++++++++++++++++++++++++++++-----
 1 file changed, 33 insertions(+), 5 deletions(-)

diff --git a/block/blk-iocost.c b/block/blk-iocost.c
index 96a6f2292623..708a43a7c6a0 100644
--- a/block/blk-iocost.c
+++ b/block/blk-iocost.c
@@ -324,6 +324,7 @@ enum ioc_running {
 enum {
 	QOS_ENABLE,
 	QOS_CTRL,
+	QOS_FREE,
 	NR_QOS_CTRL_PARAMS,
 };
 
@@ -2847,11 +2848,9 @@ static void ioc_rqos_queue_depth_changed(struct rq_qos *rqos)
 	spin_unlock_irq(&ioc->lock);
 }
 
-static void ioc_rqos_exit(struct rq_qos *rqos)
+static void __ioc_exit(struct ioc *ioc)
 {
-	struct ioc *ioc = rqos_to_ioc(rqos);
-
-	blkcg_deactivate_policy(rqos->disk, &blkcg_policy_iocost);
+	blkcg_deactivate_policy(ioc->rqos.disk, &blkcg_policy_iocost);
 
 	spin_lock_irq(&ioc->lock);
 	ioc->running = IOC_STOP;
@@ -2862,6 +2861,13 @@ static void ioc_rqos_exit(struct rq_qos *rqos)
 	kfree(ioc);
 }
 
+static void ioc_rqos_exit(struct rq_qos *rqos)
+{
+	struct ioc *ioc = rqos_to_ioc(rqos);
+
+	__ioc_exit(ioc);
+}
+
 static const struct rq_qos_ops ioc_rqos_ops = {
 	.throttle = ioc_rqos_throttle,
 	.merge = ioc_rqos_merge,
@@ -3193,6 +3199,7 @@ static int ioc_qos_show(struct seq_file *sf, void *v)
 static const match_table_t qos_ctrl_tokens = {
 	{ QOS_ENABLE,		"enable=%u"	},
 	{ QOS_CTRL,		"ctrl=%s"	},
+	{ QOS_FREE,		"free"		},
 	{ NR_QOS_CTRL_PARAMS,	NULL		},
 };
 
@@ -3210,6 +3217,7 @@ struct ioc_qos_params {
 	u32 qos[NR_QOS_PARAMS];
 	bool enable;
 	bool user;
+	bool free;
 };
 
 static void ioc_qos_params_init(struct ioc *ioc, struct ioc_qos_params *params)
@@ -3228,6 +3236,8 @@ static void ioc_qos_params_init(struct ioc *ioc, struct ioc_qos_params *params)
 		params->enable = false;
 		params->user = false;
 	}
+
+	params->free = false;
 }
 
 static int ioc_qos_params_parse(struct blkg_conf_ctx *ctx,
@@ -3260,6 +3270,9 @@ static int ioc_qos_params_parse(struct blkg_conf_ctx *ctx,
 			else
 				return -EINVAL;
 			continue;
+		case QOS_FREE:
+			params->free = true;
+			continue;
 		}
 
 		tok = match_token(p, qos_tokens, args);
@@ -3338,6 +3351,15 @@ static void ioc_qos_params_update(struct gendisk *disk, struct ioc *ioc,
 	ioc_refresh_params(ioc, true);
 }
 
+static void ioc_free(struct ioc *ioc)
+{
+	if (!ioc)
+		return;
+
+	rq_qos_del(&ioc->rqos);
+	__ioc_exit(ioc);
+}
+
 static ssize_t ioc_qos_write(struct kernfs_open_file *of, char *input,
 			     size_t nbytes, loff_t off)
 {
@@ -3366,7 +3388,7 @@ static ssize_t ioc_qos_write(struct kernfs_open_file *of, char *input,
 	if (ret)
 		goto err;
 
-	if (!ioc) {
+	if (!params.free && !ioc) {
 		ret = blk_iocost_init(disk);
 		if (ret)
 			goto err;
@@ -3376,6 +3398,11 @@ static ssize_t ioc_qos_write(struct kernfs_open_file *of, char *input,
 	blk_mq_freeze_queue(disk->queue);
 	blk_mq_quiesce_queue(disk->queue);
 
+	if (params.free) {
+		ioc_free(ioc);
+		goto out;
+	}
+
 	spin_lock_irq(&ioc->lock);
 
 	ioc_qos_params_update(disk, ioc, &params);
@@ -3386,6 +3413,7 @@ static ssize_t ioc_qos_write(struct kernfs_open_file *of, char *input,
 	else
 		wbt_enable_default(disk);
 
+out:
 	blk_mq_unquiesce_queue(disk->queue);
 	blk_mq_unfreeze_queue(disk->queue);
 
-- 
2.39.2