blkcg: remove blkcg->id

blkcg->id is a unique id given to each blkcg; however, the
cgroup_subsys_state which each blkcg embeds already has ->serial_nr
which can be used for the same purpose.  Drop blkcg->id and replace
its uses with blkcg->css.serial_nr.  Rename cfq_cgroup->blkcg_id to
->blkcg_serial_nr and @id in check_blkcg_changed() to @serial_nr for
consistency.

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

3 files changed, 5 insertions, 10 deletions

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index e17da947f6bd..0ac817b750db 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -822,7 +822,6 @@ static void blkcg_css_free(struct cgroup_subsys_state *css)
 static struct cgroup_subsys_state *
 blkcg_css_alloc(struct cgroup_subsys_state *parent_css)
 {
-        static atomic64_t id_seq = ATOMIC64_INIT(0);
         struct blkcg *blkcg;
 
         if (!parent_css) {
@@ -836,7 +835,6 @@ blkcg_css_alloc(struct cgroup_subsys_state *parent_css)
 
         blkcg->cfq_weight = CFQ_WEIGHT_DEFAULT;
         blkcg->cfq_leaf_weight = CFQ_WEIGHT_DEFAULT;
-        blkcg->id = atomic64_inc_return(&id_seq); /* root is 0, start from 1 */
 done:
         spin_lock_init(&blkcg->lock);
         INIT_RADIX_TREE(&blkcg->blkg_tree, GFP_ATOMIC);
diff --git a/block/blk-cgroup.h b/block/blk-cgroup.h
index d3fd7aa3d2a3..c567865b5f1d 100644
--- a/block/blk-cgroup.h
+++ b/block/blk-cgroup.h
@@ -50,9 +50,6 @@ struct blkcg {
         struct blkcg_gq                 *blkg_hint;
         struct hlist_head               blkg_list;
 
-        /* for policies to test whether associated blkcg has changed */
-        uint64_t                        id;
-
         /* TODO: per-policy storage in blkcg */
         unsigned int                    cfq_weight;     /* belongs to cfq */
         unsigned int                    cfq_leaf_weight;
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index cadc37841744..900f569afcc5 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -299,7 +299,7 @@ struct cfq_io_cq {
         struct cfq_ttime        ttime;
         int                     ioprio;         /* the current ioprio */
 #ifdef CONFIG_CFQ_GROUP_IOSCHED
-        uint64_t                blkcg_id;       /* the current blkcg ID */
+        uint64_t                blkcg_serial_nr; /* the current blkcg serial */
 #endif
 };
 
@@ -3534,17 +3534,17 @@ static void check_blkcg_changed(struct cfq_io_cq *cic, struct bio *bio)
 {
         struct cfq_data *cfqd = cic_to_cfqd(cic);
         struct cfq_queue *sync_cfqq;
-        uint64_t id;
+        uint64_t serial_nr;
 
         rcu_read_lock();
-        id = bio_blkcg(bio)->id;
+        serial_nr = bio_blkcg(bio)->css.serial_nr;
         rcu_read_unlock();
 
         /*
          * Check whether blkcg has changed.  The condition may trigger
          * spuriously on a newly created cic but there's no harm.
          */
-        if (unlikely(!cfqd) || likely(cic->blkcg_id == id))
+        if (unlikely(!cfqd) || likely(cic->blkcg_serial_nr == serial_nr))
                 return;
 
         sync_cfqq = cic_to_cfqq(cic, 1);
@@ -3558,7 +3558,7 @@ static void check_blkcg_changed(struct cfq_io_cq *cic, struct bio *bio)
                 cfq_put_queue(sync_cfqq);
         }
 
-        cic->blkcg_id = id;
+        cic->blkcg_serial_nr = serial_nr;
 }
 #else
 static inline void check_blkcg_changed(struct cfq_io_cq *cic, struct bio *bio) { }