[PATCH] io-controller: Get rid of css id from io cgroup

[Gui Jianfeng <guijianfeng-BthXqXjhjHXQFUHtdCDX3A@public.gmane.org>]

Get rid of css id from io cgroup since it's nothing
more than keeping track of iocg. An alternative is
caching iocg pointer in io group, just remove the
complexity.

Signed-off-by: Gui Jianfeng <guijianfeng-BthXqXjhjHXQFUHtdCDX3A@public.gmane.org>
---
 block/elevator-fq.c |   36 ++++++++++++------------------------
 block/elevator-fq.h |    2 +-
 2 files changed, 13 insertions(+), 25 deletions(-)

diff --git a/block/elevator-fq.c b/block/elevator-fq.c
index 7c83d1e..f499b54 100644
--- a/block/elevator-fq.c
+++ b/block/elevator-fq.c
@@ -191,25 +191,19 @@ static inline struct io_group *iog_parent(struct io_group *iog)
 #ifdef CONFIG_DEBUG_GROUP_IOSCHED
 static void io_group_path(struct io_group *iog, char *buf, int buflen)
 {
-	unsigned short id = iog->iocg_id;
-	struct cgroup_subsys_state *css;
+	struct io_cgroup *iocg;
+	int ret;
 
 	rcu_read_lock();
 
-	if (!id)
+	iocg = iog->iocg;
+	if (!iocg)
 		goto out;
 
-	css = css_lookup(&io_subsys, id);
-	if (!css)
-		goto out;
-
-	if (!css_tryget(css))
+	ret = cgroup_path(iocg->css.cgroup, buf, buflen);
+	if (ret)
 		goto out;
 
-	cgroup_path(css->cgroup, buf, buflen);
-
-	css_put(css);
-
 	rcu_read_unlock();
 	return;
 out:
@@ -1847,7 +1841,6 @@ struct cgroup_subsys io_subsys = {
 	.destroy = iocg_destroy,
 	.populate = iocg_populate,
 	.subsys_id = io_subsys_id,
-	.use_id = 1,
 };
 
 static inline unsigned int iog_weight(struct io_group *iog)
@@ -1890,7 +1883,7 @@ io_group_chain_alloc(struct request_queue *q, void *key, struct cgroup *cgroup)
 		if (!iog)
 			goto cleanup;
 
-		iog->iocg_id = css_id(&iocg->css);
+		iog->iocg = iocg;
 
 		sscanf(dev_name(bdi->dev), "%u:%u", &major, &minor);
 		iog->dev = MKDEV(major, minor);
@@ -2201,7 +2194,7 @@ static struct io_group *io_alloc_root_group(struct request_queue *q,
 	spin_lock_irq(&iocg->lock);
 	rcu_assign_pointer(iog->key, key);
 	hlist_add_head_rcu(&iog->group_node, &iocg->group_data);
-	iog->iocg_id = css_id(&iocg->css);
+	iog->iocg = iocg;
 	spin_unlock_irq(&iocg->lock);
 
 #ifdef CONFIG_DEBUG_GROUP_IOSCHED
@@ -2397,7 +2390,7 @@ remove_entry:
 			  group_node);
 	efqd = rcu_dereference(iog->key);
 	hlist_del_rcu(&iog->group_node);
-	iog->iocg_id = 0;
+	iog->iocg = NULL;
 	spin_unlock_irqrestore(&iocg->lock, flags);
 
 	spin_lock_irqsave(efqd->queue->queue_lock, flags);
@@ -2411,7 +2404,6 @@ done:
 		kfree(pn);
 	}
 
-	free_css_id(&io_subsys, &iocg->css);
 	rcu_read_unlock();
 	BUG_ON(!hlist_empty(&iocg->group_data));
 	kfree(iocg);
@@ -2427,20 +2419,16 @@ static void io_group_check_and_destroy(struct elv_fq_data *efqd,
 {
 	struct io_cgroup *iocg;
 	unsigned long flags;
-	struct cgroup_subsys_state *css;
 
 	rcu_read_lock();
 
-	css = css_lookup(&io_subsys, iog->iocg_id);
-
-	if (!css)
+	iocg = iog->iocg;
+	if (!iocg)
 		goto out;
 
-	iocg = container_of(css, struct io_cgroup, css);
-
 	spin_lock_irqsave(&iocg->lock, flags);
 
-	if (iog->iocg_id) {
+	if (iog->iocg) {
 		hlist_del_rcu(&iog->group_node);
 		__io_destroy_group(efqd, iog);
 	}
diff --git a/block/elevator-fq.h b/block/elevator-fq.h
index f089a55..75fee82 100644
--- a/block/elevator-fq.h
+++ b/block/elevator-fq.h
@@ -251,7 +251,7 @@ struct io_group {
 	unsigned int busy_rt_queues;
 
 	int deleting;
-	unsigned short iocg_id;
+	struct io_cgroup *iocg;
 
 	/* The device MKDEV(major, minor), this group has been created for */
 	dev_t	dev;
-- 
1.5.4.rc3