blk-cgroup: move congestion_count to struct blkcg

The congestion_count was introduced into the struct cgroup by
commit d09d8df ("blkcg: add generic throttling mechanism"),
but since it is closely related to the blkio subsys, it is not
appropriate to put it in the struct cgroup, so let's move it to
struct blkcg. There should be no functional changes because blkcg
is per cgroup.

Signed-off-by: Xiu Jianfeng <xiujianfeng@huawei.com>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20240716133058.3491350-1-xiujianfeng@huawei.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-cgroup.c

@@ -2182,12 +2182,13 @@ void blk_cgroup_bio_start(struct bio *bio)
 
 bool blk_cgroup_congested(void)
 {
-	struct cgroup_subsys_state *css;
+	struct blkcg *blkcg;
 	bool ret = false;
 
 	rcu_read_lock();
-	for (css = blkcg_css(); css; css = css->parent) {
-		if (atomic_read(&css->cgroup->congestion_count)) {
+	for (blkcg = css_to_blkcg(blkcg_css()); blkcg;
+	     blkcg = blkcg_parent(blkcg)) {
+		if (atomic_read(&blkcg->congestion_count)) {
 			ret = true;
 			break;
 		}

block/blk-cgroup.h

@@ -95,6 +95,8 @@ struct blkcg {
 	struct cgroup_subsys_state	css;
 	spinlock_t			lock;
 	refcount_t			online_pin;
+	/* If there is block congestion on this cgroup. */
+	atomic_t			congestion_count;
 
 	struct radix_tree_root		blkg_tree;
 	struct blkcg_gq	__rcu		*blkg_hint;
@@ -374,7 +376,7 @@ static inline void blkcg_use_delay(struct blkcg_gq *blkg)
 	if (WARN_ON_ONCE(atomic_read(&blkg->use_delay) < 0))
 		return;
 	if (atomic_add_return(1, &blkg->use_delay) == 1)
-		atomic_inc(&blkg->blkcg->css.cgroup->congestion_count);
+		atomic_inc(&blkg->blkcg->congestion_count);
 }
 
 static inline int blkcg_unuse_delay(struct blkcg_gq *blkg)
@@ -399,7 +401,7 @@ static inline int blkcg_unuse_delay(struct blkcg_gq *blkg)
 	if (old == 0)
 		return 0;
 	if (old == 1)
-		atomic_dec(&blkg->blkcg->css.cgroup->congestion_count);
+		atomic_dec(&blkg->blkcg->congestion_count);
 	return 1;
 }
 
@@ -418,7 +420,7 @@ static inline void blkcg_set_delay(struct blkcg_gq *blkg, u64 delay)
 
 	/* We only want 1 person setting the congestion count for this blkg. */
 	if (!old && atomic_try_cmpxchg(&blkg->use_delay, &old, -1))
-		atomic_inc(&blkg->blkcg->css.cgroup->congestion_count);
+		atomic_inc(&blkg->blkcg->congestion_count);
 
 	atomic64_set(&blkg->delay_nsec, delay);
 }
@@ -435,7 +437,7 @@ static inline void blkcg_clear_delay(struct blkcg_gq *blkg)
 
 	/* We only want 1 person clearing the congestion count for this blkg. */
 	if (old && atomic_try_cmpxchg(&blkg->use_delay, &old, 0))
-		atomic_dec(&blkg->blkcg->css.cgroup->congestion_count);
+		atomic_dec(&blkg->blkcg->congestion_count);
 }
 
 /**

include/linux/cgroup-defs.h

@@ -534,9 +534,6 @@ struct cgroup {
 	/* used to store eBPF programs */
 	struct cgroup_bpf bpf;
 
-	/* If there is block congestion on this cgroup. */
-	atomic_t congestion_count;
-
 	/* Used to store internal freezer state */
 	struct cgroup_freezer_state freezer;