blkcg: move per-queue blkg list heads and counters to queue and blkg

Currently, specific policy implementations are responsible for
maintaining list and number of blkgs.  This duplicates code
unnecessarily, and hinders factoring common code and providing blkcg
API with better defined semantics.

After this patch, request_queue hosts list heads and counters and blkg
has list nodes for both policies.  This patch only relocates the
necessary fields and the next patch will actually move management code
into blkcg core.

Note that request_queue->blkg_list[] and ->nr_blkgs[] are hardcoded to
have 2 elements.  This is to avoid include dependency and will be
removed by the next patch.

This patch doesn't introduce any behavior change.

-v2: Now unnecessary conditional on CONFIG_BLK_CGROUP_MODULE removed
     as pointed out by Vivek.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 19 insertions, 28 deletions

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 11dd9d7f2edb..e846803280a6 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -208,9 +208,7 @@ struct cfq_group {
 	unsigned long saved_workload_slice;
 	enum wl_type_t saved_workload;
 	enum wl_prio_t saved_serving_prio;
-#ifdef CONFIG_CFQ_GROUP_IOSCHED
-	struct hlist_node cfqd_node;
-#endif
+
 	/* number of requests that are on the dispatch list or inside driver */
 	int dispatched;
 	struct cfq_ttime ttime;
@@ -302,12 +300,6 @@ struct cfq_data {
 	struct cfq_queue oom_cfqq;
 
 	unsigned long last_delayed_sync;
-
-	/* List of cfq groups being managed on this device*/
-	struct hlist_head cfqg_list;
-
-	/* Number of groups which are on blkcg->blkg_list */
-	unsigned int nr_blkcg_linked_grps;
 };
 
 static inline struct cfq_group *blkg_to_cfqg(struct blkio_group *blkg)
@@ -1056,13 +1048,9 @@ static void cfq_update_blkio_group_weight(struct request_queue *q,
 static void cfq_link_blkio_group(struct request_queue *q,
 				 struct blkio_group *blkg)
 {
-	struct cfq_data *cfqd = q->elevator->elevator_data;
-	struct cfq_group *cfqg = blkg_to_cfqg(blkg);
-
-	cfqd->nr_blkcg_linked_grps++;
-
-	/* Add group on cfqd list */
-	hlist_add_head(&cfqg->cfqd_node, &cfqd->cfqg_list);
+	list_add(&blkg->q_node[BLKIO_POLICY_PROP],
+		 &q->blkg_list[BLKIO_POLICY_PROP]);
+	q->nr_blkgs[BLKIO_POLICY_PROP]++;
 }
 
 static void cfq_init_blkio_group(struct blkio_group *blkg)
@@ -1110,13 +1098,15 @@ static void cfq_link_cfqq_cfqg(struct cfq_queue *cfqq, struct cfq_group *cfqg)
 
 static void cfq_destroy_cfqg(struct cfq_data *cfqd, struct cfq_group *cfqg)
 {
+	struct blkio_group *blkg = cfqg_to_blkg(cfqg);
+
 	/* Something wrong if we are trying to remove same group twice */
-	BUG_ON(hlist_unhashed(&cfqg->cfqd_node));
+	BUG_ON(list_empty(&blkg->q_node[BLKIO_POLICY_PROP]));
 
-	hlist_del_init(&cfqg->cfqd_node);
+	list_del_init(&blkg->q_node[BLKIO_POLICY_PROP]);
 
-	BUG_ON(cfqd->nr_blkcg_linked_grps <= 0);
-	cfqd->nr_blkcg_linked_grps--;
+	BUG_ON(cfqd->queue->nr_blkgs[BLKIO_POLICY_PROP] <= 0);
+	cfqd->queue->nr_blkgs[BLKIO_POLICY_PROP]--;
 
 	/*
 	 * Put the reference taken at the time of creation so that when all
@@ -1127,18 +1117,19 @@ static void cfq_destroy_cfqg(struct cfq_data *cfqd, struct cfq_group *cfqg)
 
 static bool cfq_release_cfq_groups(struct cfq_data *cfqd)
 {
-	struct hlist_node *pos, *n;
-	struct cfq_group *cfqg;
+	struct request_queue *q = cfqd->queue;
+	struct blkio_group *blkg, *n;
 	bool empty = true;
 
-	hlist_for_each_entry_safe(cfqg, pos, n, &cfqd->cfqg_list, cfqd_node) {
+	list_for_each_entry_safe(blkg, n, &q->blkg_list[BLKIO_POLICY_PROP],
+				 q_node[BLKIO_POLICY_PROP]) {
 		/*
 		 * If cgroup removal path got to blk_group first and removed
 		 * it from cgroup list, then it will take care of destroying
 		 * cfqg also.
 		 */
-		if (!cfq_blkiocg_del_blkio_group(cfqg_to_blkg(cfqg)))
-			cfq_destroy_cfqg(cfqd, cfqg);
+		if (!cfq_blkiocg_del_blkio_group(blkg))
+			cfq_destroy_cfqg(cfqd, blkg_to_cfqg(blkg));
 		else
 			empty = false;
 	}
@@ -3558,13 +3549,13 @@ static void cfq_exit_queue(struct elevator_queue *e)
 	cfq_put_async_queues(cfqd);
 	cfq_release_cfq_groups(cfqd);
 
+#ifdef CONFIG_BLK_CGROUP
 	/*
 	 * If there are groups which we could not unlink from blkcg list,
 	 * wait for a rcu period for them to be freed.
 	 */
-	if (cfqd->nr_blkcg_linked_grps)
-		wait = true;
-
+	wait = q->nr_blkgs[BLKIO_POLICY_PROP];
+#endif
 	spin_unlock_irq(q->queue_lock);
 
 	cfq_shutdown_timer_wq(cfqd);