Message-Id: <1328131156-13290-12-git-send-email-tj@kernel.org>
Date:	Wed,  1 Feb 2012 13:19:16 -0800
From:	Tejun Heo <tj@...nel.org>
To:	axboe@...nel.dk, vgoyal@...hat.com
Cc:	ctalbott@...gle.com, rni@...gle.com, linux-kernel@...r.kernel.org,
	Tejun Heo <tj@...nel.org>
Subject: [PATCH 11/11] blkcg: unify blkg's for blkcg policies

Currently, blkg is per cgroup-queue-policy combination.  This is
unnatural and leads to various convolutions in partially used
duplicate fields in blkg, config / stat access, and general management
of blkgs.

This patch make blkg's per cgroup-queue and let them serve all
policies.  blkgs are now created and destroyed by blkcg core proper.
This will allow further consolidation of common management logic into
blkcg core and API with better defined semantics and layering.

As a transitional step to untangle blkg management, elvswitch and
policy [de]registration, all blkgs except the root blkg are being shot
down during elvswitch and bypass.  This patch adds blkg_root_update()
to update root blkg in place on policy change.  This is hacky but
should be good enough as interim step until we get locking simplified
and switch over to in-place update for all blkgs.

Signed-off-by: Tejun Heo <tj@...nel.org>
Cc: Vivek Goyal <vgoyal@...hat.com>
---
 block/blk-cgroup.c     |  215 +++++++++++++++++++++++++++++-------------------
 block/blk-cgroup.h     |   10 +--
 block/blk-core.c       |    3 +-
 block/blk-sysfs.c      |    4 +-
 block/blk-throttle.c   |    9 +--
 block/cfq-iosched.c    |    4 +-
 block/elevator.c       |    5 +-
 include/linux/blkdev.h |    5 +-
 8 files changed, 146 insertions(+), 109 deletions(-)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index a7f9363..ae988f0 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -461,16 +461,20 @@ EXPORT_SYMBOL_GPL(blkiocg_update_io_merged_stats);
  */
 static void blkg_free(struct blkio_group *blkg)
 {
-	struct blkg_policy_data *pd;
+	int i;
 
 	if (!blkg)
 		return;
 
-	pd = blkg->pd[blkg->plid];
-	if (pd) {
-		free_percpu(pd->stats_cpu);
-		kfree(pd);
+	for (i = 0; i < BLKIO_NR_POLICIES; i++) {
+		struct blkg_policy_data *pd = blkg->pd[i];
+
+		if (pd) {
+			free_percpu(pd->stats_cpu);
+			kfree(pd);
+		}
 	}
+
 	kfree(blkg);
 }
 
@@ -486,11 +490,10 @@ static void blkg_free(struct blkio_group *blkg)
  *        percpu stat breakage.
  */
 static struct blkio_group *blkg_alloc(struct blkio_cgroup *blkcg,
-				      struct request_queue *q,
-				      struct blkio_policy_type *pol)
+				      struct request_queue *q)
 {
 	struct blkio_group *blkg;
-	struct blkg_policy_data *pd;
+	int i;
 
 	/* alloc and init base part */
 	blkg = kzalloc_node(sizeof(*blkg), GFP_ATOMIC, q->node);
@@ -499,34 +502,83 @@ static struct blkio_group *blkg_alloc(struct blkio_cgroup *blkcg,
 
 	spin_lock_init(&blkg->stats_lock);
 	rcu_assign_pointer(blkg->q, q);
-	INIT_LIST_HEAD(&blkg->q_node[0]);
-	INIT_LIST_HEAD(&blkg->q_node[1]);
+	INIT_LIST_HEAD(&blkg->q_node);
 	blkg->blkcg = blkcg;
-	blkg->plid = pol->plid;
 	blkg->refcnt = 1;
 	cgroup_path(blkcg->css.cgroup, blkg->path, sizeof(blkg->path));
 
-	/* alloc per-policy data and attach it to blkg */
-	pd = kzalloc_node(sizeof(*pd) + pol->pdata_size, GFP_ATOMIC,
-			  q->node);
-	if (!pd) {
-		blkg_free(blkg);
-		return NULL;
+	for (i = 0; i < BLKIO_NR_POLICIES; i++) {
+		struct blkio_policy_type *pol = blkio_policy[i];
+		struct blkg_policy_data *pd;
+
+		if (!pol)
+			continue;
+
+		/* alloc per-policy data and attach it to blkg */
+		pd = kzalloc_node(sizeof(*pd) + pol->pdata_size, GFP_ATOMIC,
+				  q->node);
+		if (!pd) {
+			blkg_free(blkg);
+			return NULL;
+		}
+
+		blkg->pd[i] = pd;
+		pd->blkg = blkg;
+
+		/* broken, read comment in the callsite */
+		pd->stats_cpu = alloc_percpu(struct blkio_group_stats_cpu);
+		if (!pd->stats_cpu) {
+			blkg_free(blkg);
+			return NULL;
+		}
 	}
 
-	blkg->pd[pol->plid] = pd;
-	pd->blkg = blkg;
+	/* invoke per-policy init */
+	for (i = 0; i < BLKIO_NR_POLICIES; i++) {
+		struct blkio_policy_type *pol = blkio_policy[i];
+
+		if (pol)
+			pol->ops.blkio_init_group_fn(blkg);
+	}
+
+	return blkg;
+}
+
+/*
+ * XXX: This updates blkg policy data in-place for root blkg, which is
+ * necessary across policy registration as root blkgs aren't shot down.
+ * This hacky implementation is interim.  Eventually, blkg shoot down will
+ * be replaced by proper in-place update.
+ */
+static struct blkio_group *blkg_root_update(struct blkio_group *blkg,
+					    enum blkio_policy_id plid)
+{
+	struct request_queue *q = blkg->q;
+	struct blkio_policy_type *pol = blkio_policy[plid];
+	struct blkg_policy_data *pd;
 
-	/* broken, read comment in the callsite */
+	kfree(blkg->pd[plid]);
+	blkg->pd[plid] = NULL;
 
+	pd = kzalloc(sizeof(*pd) + pol->pdata_size, GFP_ATOMIC);
+	if (!pd)
+		return NULL;
+
+	spin_unlock_irq(q->queue_lock);
+	rcu_read_unlock();
 	pd->stats_cpu = alloc_percpu(struct blkio_group_stats_cpu);
+	rcu_read_lock();
+	spin_lock_irq(q->queue_lock);
+
 	if (!pd->stats_cpu) {
-		blkg_free(blkg);
+		kfree(pd);
 		return NULL;
 	}
 
-	/* invoke per-policy init */
+	blkg->pd[plid] = pd;
+	pd->blkg = blkg;
 	pol->ops.blkio_init_group_fn(blkg);
+
 	return blkg;
 }
 
@@ -536,7 +588,6 @@ struct blkio_group *blkg_lookup_create(struct blkio_cgroup *blkcg,
 				       bool for_root)
 	__releases(q->queue_lock) __acquires(q->queue_lock)
 {
-	struct blkio_policy_type *pol = blkio_policy[plid];
 	struct blkio_group *blkg, *new_blkg;
 
 	WARN_ON_ONCE(!rcu_read_lock_held());
@@ -551,9 +602,12 @@ struct blkio_group *blkg_lookup_create(struct blkio_cgroup *blkcg,
 	if (unlikely(blk_queue_bypass(q)) && !for_root)
 		return ERR_PTR(blk_queue_dead(q) ? -EINVAL : -EBUSY);
 
-	blkg = blkg_lookup(blkcg, q, plid);
-	if (blkg)
+	blkg = blkg_lookup(blkcg, q);
+	if (blkg) {
+		if (for_root)
+			return blkg_root_update(blkg, plid);
 		return blkg;
+	}
 
 	/* blkg holds a reference to blkcg */
 	if (!css_tryget(&blkcg->css))
@@ -571,7 +625,7 @@ struct blkio_group *blkg_lookup_create(struct blkio_cgroup *blkcg,
 	spin_unlock_irq(q->queue_lock);
 	rcu_read_unlock();
 
-	new_blkg = blkg_alloc(blkcg, q, pol);
+	new_blkg = blkg_alloc(blkcg, q);
 
 	rcu_read_lock();
 	spin_lock_irq(q->queue_lock);
@@ -583,7 +637,7 @@ struct blkio_group *blkg_lookup_create(struct blkio_cgroup *blkcg,
 	}
 
 	/* did someone beat us to it? */
-	blkg = blkg_lookup(blkcg, q, plid);
+	blkg = blkg_lookup(blkcg, q);
 	if (unlikely(blkg))
 		goto out;
 
@@ -598,8 +652,8 @@ struct blkio_group *blkg_lookup_create(struct blkio_cgroup *blkcg,
 	swap(blkg, new_blkg);
 
 	hlist_add_head_rcu(&blkg->blkcg_node, &blkcg->blkg_list);
-	list_add(&blkg->q_node[plid], &q->blkg_list[plid]);
-	q->nr_blkgs[plid]++;
+	list_add(&blkg->q_node, &q->blkg_list);
+	q->nr_blkgs++;
 
 	spin_unlock(&blkcg->lock);
 out:
@@ -636,31 +690,30 @@ EXPORT_SYMBOL_GPL(blkiocg_del_blkio_group);
 
 /* called under rcu_read_lock(). */
 struct blkio_group *blkg_lookup(struct blkio_cgroup *blkcg,
-				struct request_queue *q,
-				enum blkio_policy_id plid)
+				struct request_queue *q)
 {
 	struct blkio_group *blkg;
 	struct hlist_node *n;
 
 	hlist_for_each_entry_rcu(blkg, n, &blkcg->blkg_list, blkcg_node)
-		if (blkg->q == q && blkg->plid == plid)
+		if (blkg->q == q)
 			return blkg;
 	return NULL;
 }
 EXPORT_SYMBOL_GPL(blkg_lookup);
 
-static void blkg_destroy(struct blkio_group *blkg, enum blkio_policy_id plid)
+static void blkg_destroy(struct blkio_group *blkg)
 {
 	struct request_queue *q = blkg->q;
 
 	lockdep_assert_held(q->queue_lock);
 
 	/* Something wrong if we are trying to remove same group twice */
-	WARN_ON_ONCE(list_empty(&blkg->q_node[plid]));
-	list_del_init(&blkg->q_node[plid]);
+	WARN_ON_ONCE(list_empty(&blkg->q_node));
+	list_del_init(&blkg->q_node);
 
-	WARN_ON_ONCE(q->nr_blkgs[plid] <= 0);
-	q->nr_blkgs[plid]--;
+	WARN_ON_ONCE(q->nr_blkgs <= 0);
+	q->nr_blkgs--;
 
 	/*
 	 * Put the reference taken at the time of creation so that when all
@@ -669,8 +722,7 @@ static void blkg_destroy(struct blkio_group *blkg, enum blkio_policy_id plid)
 	blkg_put(blkg);
 }
 
-void blkg_destroy_all(struct request_queue *q, enum blkio_policy_id plid,
-		      bool destroy_root)
+void blkg_destroy_all(struct request_queue *q, bool destroy_root)
 {
 	struct blkio_group *blkg, *n;
 
@@ -679,8 +731,7 @@ void blkg_destroy_all(struct request_queue *q, enum blkio_policy_id plid,
 
 		spin_lock_irq(q->queue_lock);
 
-		list_for_each_entry_safe(blkg, n, &q->blkg_list[plid],
-					 q_node[plid]) {
+		list_for_each_entry_safe(blkg, n, &q->blkg_list, q_node) {
 			/* skip root? */
 			if (!destroy_root && blkg->blkcg == &blkio_root_cgroup)
 				continue;
@@ -691,7 +742,7 @@ void blkg_destroy_all(struct request_queue *q, enum blkio_policy_id plid,
 			 * take care of destroying cfqg also.
 			 */
 			if (!blkiocg_del_blkio_group(blkg))
-				blkg_destroy(blkg, plid);
+				blkg_destroy(blkg);
 			else
 				done = false;
 		}
@@ -776,43 +827,49 @@ blkiocg_reset_stats(struct cgroup *cgroup, struct cftype *cftype, u64 val)
 #endif
 
 	blkcg = cgroup_to_blkio_cgroup(cgroup);
+	spin_lock(&blkio_list_lock);
 	spin_lock_irq(&blkcg->lock);
 	hlist_for_each_entry(blkg, n, &blkcg->blkg_list, blkcg_node) {
-		struct blkg_policy_data *pd = blkg->pd[blkg->plid];
+		struct blkio_policy_type *pol;
+
+		list_for_each_entry(pol, &blkio_list, list) {
+			struct blkg_policy_data *pd = blkg->pd[pol->plid];
 
-		spin_lock(&blkg->stats_lock);
-		stats = &pd->stats;
+			spin_lock(&blkg->stats_lock);
+			stats = &pd->stats;
 #ifdef CONFIG_DEBUG_BLK_CGROUP
-		idling = blkio_blkg_idling(stats);
-		waiting = blkio_blkg_waiting(stats);
-		empty = blkio_blkg_empty(stats);
+			idling = blkio_blkg_idling(stats);
+			waiting = blkio_blkg_waiting(stats);
+			empty = blkio_blkg_empty(stats);
 #endif
-		for (i = 0; i < BLKIO_STAT_TOTAL; i++)
-			queued[i] = stats->stat_arr[BLKIO_STAT_QUEUED][i];
-		memset(stats, 0, sizeof(struct blkio_group_stats));
-		for (i = 0; i < BLKIO_STAT_TOTAL; i++)
-			stats->stat_arr[BLKIO_STAT_QUEUED][i] = queued[i];
+			for (i = 0; i < BLKIO_STAT_TOTAL; i++)
+				queued[i] = stats->stat_arr[BLKIO_STAT_QUEUED][i];
+			memset(stats, 0, sizeof(struct blkio_group_stats));
+			for (i = 0; i < BLKIO_STAT_TOTAL; i++)
+				stats->stat_arr[BLKIO_STAT_QUEUED][i] = queued[i];
 #ifdef CONFIG_DEBUG_BLK_CGROUP
-		if (idling) {
-			blkio_mark_blkg_idling(stats);
-			stats->start_idle_time = now;
-		}
-		if (waiting) {
-			blkio_mark_blkg_waiting(stats);
-			stats->start_group_wait_time = now;
-		}
-		if (empty) {
-			blkio_mark_blkg_empty(stats);
-			stats->start_empty_time = now;
-		}
+			if (idling) {
+				blkio_mark_blkg_idling(stats);
+				stats->start_idle_time = now;
+			}
+			if (waiting) {
+				blkio_mark_blkg_waiting(stats);
+				stats->start_group_wait_time = now;
+			}
+			if (empty) {
+				blkio_mark_blkg_empty(stats);
+				stats->start_empty_time = now;
+			}
 #endif
-		spin_unlock(&blkg->stats_lock);
+			spin_unlock(&blkg->stats_lock);
 
-		/* Reset Per cpu stats which don't take blkg->stats_lock */
-		blkio_reset_stats_cpu(blkg, blkg->plid);
+			/* Reset Per cpu stats which don't take blkg->stats_lock */
+			blkio_reset_stats_cpu(blkg, pol->plid);
+		}
 	}
 
 	spin_unlock_irq(&blkcg->lock);
+	spin_unlock(&blkio_list_lock);
 	return 0;
 }
 
@@ -1157,8 +1214,7 @@ static void blkio_read_conf(struct cftype *cft, struct blkio_cgroup *blkcg,
 
 	spin_lock_irq(&blkcg->lock);
 	hlist_for_each_entry(blkg, n, &blkcg->blkg_list, blkcg_node)
-		if (BLKIOFILE_POLICY(cft->private) == blkg->plid)
-			blkio_print_group_conf(cft, blkg, m);
+		blkio_print_group_conf(cft, blkg, m);
 	spin_unlock_irq(&blkcg->lock);
 }
 
@@ -1213,8 +1269,6 @@ static int blkio_read_blkg_stats(struct blkio_cgroup *blkcg,
 		const char *dname = dev_name(blkg->q->backing_dev_info.dev);
 		int plid = BLKIOFILE_POLICY(cft->private);
 
-		if (plid != blkg->plid)
-			continue;
 		if (pcpu) {
 			cgroup_total += blkio_get_stat_cpu(blkg, plid,
 							   cb, dname, type);
@@ -1324,9 +1378,9 @@ static int blkio_weight_write(struct blkio_cgroup *blkcg, int plid, u64 val)
 	blkcg->weight = (unsigned int)val;
 
 	hlist_for_each_entry(blkg, n, &blkcg->blkg_list, blkcg_node) {
-		struct blkg_policy_data *pd = blkg->pd[blkg->plid];
+		struct blkg_policy_data *pd = blkg->pd[plid];
 
-		if (blkg->plid == plid && !pd->conf.weight)
+		if (!pd->conf.weight)
 			blkio_update_group_weight(blkg, plid, blkcg->weight);
 	}
 
@@ -1549,7 +1603,6 @@ static int blkiocg_pre_destroy(struct cgroup_subsys *subsys,
 	unsigned long flags;
 	struct blkio_group *blkg;
 	struct request_queue *q;
-	struct blkio_policy_type *blkiop;
 
 	rcu_read_lock();
 
@@ -1575,11 +1628,7 @@ static int blkiocg_pre_destroy(struct cgroup_subsys *subsys,
 		 */
 		spin_lock(&blkio_list_lock);
 		spin_lock_irqsave(q->queue_lock, flags);
-		list_for_each_entry(blkiop, &blkio_list, list) {
-			if (blkiop->plid != blkg->plid)
-				continue;
-			blkg_destroy(blkg, blkiop->plid);
-		}
+		blkg_destroy(blkg);
 		spin_unlock_irqrestore(q->queue_lock, flags);
 		spin_unlock(&blkio_list_lock);
 	} while (1);
@@ -1673,6 +1722,8 @@ void blkcg_exit_queue(struct request_queue *q)
 	list_del_init(&q->all_q_node);
 	mutex_unlock(&all_q_mutex);
 
+	blkg_destroy_all(q, true);
+
 	blk_throtl_exit(q);
 }
 
@@ -1722,14 +1773,12 @@ static void blkcg_bypass_start(void)
 	__acquires(&all_q_mutex)
 {
 	struct request_queue *q;
-	int i;
 
 	mutex_lock(&all_q_mutex);
 
 	list_for_each_entry(q, &all_q_list, all_q_node) {
 		blk_queue_bypass_start(q);
-		for (i = 0; i < BLKIO_NR_POLICIES; i++)
-			blkg_destroy_all(q, i, false);
+		blkg_destroy_all(q, false);
 	}
 }
 
diff --git a/block/blk-cgroup.h b/block/blk-cgroup.h
index 83ce5fa..bd66936 100644
--- a/block/blk-cgroup.h
+++ b/block/blk-cgroup.h
@@ -178,13 +178,11 @@ struct blkg_policy_data {
 struct blkio_group {
 	/* Pointer to the associated request_queue, RCU protected */
 	struct request_queue __rcu *q;
-	struct list_head q_node[BLKIO_NR_POLICIES];
+	struct list_head q_node;
 	struct hlist_node blkcg_node;
 	struct blkio_cgroup *blkcg;
 	/* Store cgroup path */
 	char path[128];
-	/* policy which owns this blk group */
-	enum blkio_policy_id plid;
 	/* reference count */
 	int refcnt;
 
@@ -230,8 +228,7 @@ extern void blkcg_exit_queue(struct request_queue *q);
 /* Blkio controller policy registration */
 extern void blkio_policy_register(struct blkio_policy_type *);
 extern void blkio_policy_unregister(struct blkio_policy_type *);
-extern void blkg_destroy_all(struct request_queue *q,
-			     enum blkio_policy_id plid, bool destroy_root);
+extern void blkg_destroy_all(struct request_queue *q, bool destroy_root);
 
 /**
  * blkg_to_pdata - get policy private data
@@ -382,8 +379,7 @@ extern struct blkio_cgroup *cgroup_to_blkio_cgroup(struct cgroup *cgroup);
 extern struct blkio_cgroup *task_blkio_cgroup(struct task_struct *tsk);
 extern int blkiocg_del_blkio_group(struct blkio_group *blkg);
 extern struct blkio_group *blkg_lookup(struct blkio_cgroup *blkcg,
-				       struct request_queue *q,
-				       enum blkio_policy_id plid);
+				       struct request_queue *q);
 struct blkio_group *blkg_lookup_create(struct blkio_cgroup *blkcg,
 				       struct request_queue *q,
 				       enum blkio_policy_id plid,
diff --git a/block/blk-core.c b/block/blk-core.c
index 025ef60..6de6cb5 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -547,8 +547,7 @@ struct request_queue *blk_alloc_queue_node(gfp_t gfp_mask, int node_id)
 	INIT_LIST_HEAD(&q->timeout_list);
 	INIT_LIST_HEAD(&q->icq_list);
 #if defined(CONFIG_BLK_CGROUP) || defined(CONFIG_BLK_CGROUP_MODULE)
-	INIT_LIST_HEAD(&q->blkg_list[0]);
-	INIT_LIST_HEAD(&q->blkg_list[1]);
+	INIT_LIST_HEAD(&q->blkg_list);
 #endif
 	INIT_LIST_HEAD(&q->flush_queue[0]);
 	INIT_LIST_HEAD(&q->flush_queue[1]);
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 00cdc98..aa41b47 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -480,6 +480,8 @@ static void blk_release_queue(struct kobject *kobj)
 
 	blk_sync_queue(q);
 
+	blkcg_exit_queue(q);
+
 	if (q->elevator) {
 		spin_lock_irq(q->queue_lock);
 		ioc_clear_queue(q);
@@ -487,8 +489,6 @@ static void blk_release_queue(struct kobject *kobj)
 		elevator_exit(q->elevator);
 	}
 
-	blkcg_exit_queue(q);
-
 	if (rl->rq_pool)
 		mempool_destroy(rl->rq_pool);
 
diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 1329412..e35ee7a 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -167,7 +167,7 @@ throtl_grp *throtl_lookup_tg(struct throtl_data *td, struct blkio_cgroup *blkcg)
 	if (blkcg == &blkio_root_cgroup)
 		return td->root_tg;
 
-	return blkg_to_tg(blkg_lookup(blkcg, td->queue, BLKIO_POLICY_THROTL));
+	return blkg_to_tg(blkg_lookup(blkcg, td->queue));
 }
 
 static struct throtl_grp *throtl_lookup_create_tg(struct throtl_data *td,
@@ -704,8 +704,7 @@ static void throtl_process_limit_change(struct throtl_data *td)
 
 	throtl_log(td, "limits changed");
 
-	list_for_each_entry_safe(blkg, n, &q->blkg_list[BLKIO_POLICY_THROTL],
-				 q_node[BLKIO_POLICY_THROTL]) {
+	list_for_each_entry_safe(blkg, n, &q->blkg_list, q_node) {
 		struct throtl_grp *tg = blkg_to_tg(blkg);
 
 		if (!tg->limits_changed)
@@ -1054,11 +1053,9 @@ void blk_throtl_exit(struct request_queue *q)
 
 	throtl_shutdown_wq(q);
 
-	blkg_destroy_all(q, BLKIO_POLICY_THROTL, true);
-
 	/* If there are other groups */
 	spin_lock_irq(q->queue_lock);
-	wait = q->nr_blkgs[BLKIO_POLICY_THROTL];
+	wait = q->nr_blkgs;
 	spin_unlock_irq(q->queue_lock);
 
 	/*
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 7093309..e3fa5d6 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -3468,14 +3468,12 @@ static void cfq_exit_queue(struct elevator_queue *e)
 
 	spin_unlock_irq(q->queue_lock);
 
-	blkg_destroy_all(q, BLKIO_POLICY_PROP, true);
-
 	/*
 	 * If there are groups which we could not unlink from blkcg list,
 	 * wait for a rcu period for them to be freed.
 	 */
 	spin_lock_irq(q->queue_lock);
-	wait = q->nr_blkgs[BLKIO_POLICY_PROP];
+	wait = q->nr_blkgs;
 	spin_unlock_irq(q->queue_lock);
 
 	cfq_shutdown_timer_wq(cfqd);
diff --git a/block/elevator.c b/block/elevator.c
index 4599615..49504cd 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -923,7 +923,7 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
 {
 	struct elevator_queue *old = q->elevator;
 	bool registered = old->registered;
-	int i, err;
+	int err;
 
 	/*
 	 * Turn on BYPASS and drain all requests w/ elevator private data.
@@ -942,8 +942,7 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
 	ioc_clear_queue(q);
 	spin_unlock_irq(q->queue_lock);
 
-	for (i = 0; i < BLKIO_NR_POLICIES; i++)
-		blkg_destroy_all(q, i, false);
+	blkg_destroy_all(q, false);
 
 	/* allocate, init and register new elevator */
 	err = -ENOMEM;
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 5eb8a93..f4d40bc 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -363,9 +363,8 @@ struct request_queue {
 
 	struct list_head	icq_list;
 #if defined(CONFIG_BLK_CGROUP) || defined(CONFIG_BLK_CGROUP_MODULE)
-	/* XXX: array size hardcoded to avoid include dependency (temporary) */
-	struct list_head	blkg_list[2];
-	int			nr_blkgs[2];
+	struct list_head	blkg_list;
+	int			nr_blkgs;
 #endif
 
 	struct queue_limits	limits;
-- 
1.7.7.3

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