blkcg: add request_queue->root_blkg

With per-queue policy activation, root blkg creation will be moved to
blkcg core.  Add q->root_blkg in preparation.  For blk-throtl, this
replaces throtl_data->root_tg; however, cfq needs to keep
cfqd->root_group for !CONFIG_CFQ_GROUP_IOSCHED.

This is to prepare for per-queue policy activation and doesn't cause
any functional difference.

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, 10 insertions, 6 deletions

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 6f1bfdf9a1b7..8c520fad6885 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -97,7 +97,6 @@ struct throtl_data
         /* service tree for active throtl groups */
         struct throtl_rb_root tg_service_tree;
 
-        struct throtl_grp *root_tg;
         struct request_queue *queue;
 
         /* Total Number of queued bios on READ and WRITE lists */
@@ -131,6 +130,11 @@ static inline struct blkio_group *tg_to_blkg(struct throtl_grp *tg)
         return pdata_to_blkg(tg);
 }
 
+static inline struct throtl_grp *td_root_tg(struct throtl_data *td)
+{
+        return blkg_to_tg(td->queue->root_blkg);
+}
+
 enum tg_state_flags {
         THROTL_TG_FLAG_on_rr = 0,       /* on round-robin busy list */
 };
@@ -261,7 +265,7 @@ throtl_grp *throtl_lookup_tg(struct throtl_data *td, struct blkio_cgroup *blkcg)
          * Avoid lookup in this case
          */
         if (blkcg == &blkio_root_cgroup)
-                return td->root_tg;
+                return td_root_tg(td);
 
         return blkg_to_tg(blkg_lookup(blkcg, td->queue));
 }
@@ -277,7 +281,7 @@ static struct throtl_grp *throtl_lookup_create_tg(struct throtl_data *td,
          * Avoid lookup in this case
          */
         if (blkcg == &blkio_root_cgroup) {
-                tg = td->root_tg;
+                tg = td_root_tg(td);
         } else {
                 struct blkio_group *blkg;
 
@@ -287,7 +291,7 @@ static struct throtl_grp *throtl_lookup_create_tg(struct throtl_data *td,
                 if (!IS_ERR(blkg))
                         tg = blkg_to_tg(blkg);
                 else if (!blk_queue_dead(q))
-                        tg = td->root_tg;
+                        tg = td_root_tg(td);
         }
 
         return tg;
@@ -1245,12 +1249,12 @@ int blk_throtl_init(struct request_queue *q)
 
         blkg = blkg_lookup_create(&blkio_root_cgroup, q, true);
         if (!IS_ERR(blkg))
-                td->root_tg = blkg_to_tg(blkg);
+                q->root_blkg = blkg;
 
         spin_unlock_irq(q->queue_lock);
         rcu_read_unlock();
 
-        if (!td->root_tg) {
+        if (!q->root_blkg) {
                 kfree(td);
                 return -ENOMEM;
         }