blkcg: change blkg reference counting to use percpu_ref
Now that every bio is associated with a blkg, this puts the use of blkg_get, blkg_try_get, and blkg_put on the hot path. This switches over the refcnt in blkg to use percpu_ref. Signed-off-by: Dennis Zhou <dennisszhou@gmail.com> Acked-by: Tejun Heo <tj@kernel.org> Signed-off-by: Jens Axboe <axboe@kernel.dk>
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@ -84,6 +84,37 @@ static void blkg_free(struct blkcg_gq *blkg)
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kfree(blkg);
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}
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static void __blkg_release(struct rcu_head *rcu)
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{
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struct blkcg_gq *blkg = container_of(rcu, struct blkcg_gq, rcu_head);
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percpu_ref_exit(&blkg->refcnt);
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/* release the blkcg and parent blkg refs this blkg has been holding */
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css_put(&blkg->blkcg->css);
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if (blkg->parent)
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blkg_put(blkg->parent);
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wb_congested_put(blkg->wb_congested);
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blkg_free(blkg);
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}
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/*
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* A group is RCU protected, but having an rcu lock does not mean that one
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* can access all the fields of blkg and assume these are valid. For
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* example, don't try to follow throtl_data and request queue links.
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*
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* Having a reference to blkg under an rcu allows accesses to only values
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* local to groups like group stats and group rate limits.
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*/
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static void blkg_release(struct percpu_ref *ref)
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{
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struct blkcg_gq *blkg = container_of(ref, struct blkcg_gq, refcnt);
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call_rcu(&blkg->rcu_head, __blkg_release);
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}
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/**
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* blkg_alloc - allocate a blkg
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* @blkcg: block cgroup the new blkg is associated with
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@ -110,7 +141,6 @@ static struct blkcg_gq *blkg_alloc(struct blkcg *blkcg, struct request_queue *q,
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blkg->q = q;
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INIT_LIST_HEAD(&blkg->q_node);
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blkg->blkcg = blkcg;
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atomic_set(&blkg->refcnt, 1);
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/* root blkg uses @q->root_rl, init rl only for !root blkgs */
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if (blkcg != &blkcg_root) {
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@ -217,6 +247,11 @@ static struct blkcg_gq *blkg_create(struct blkcg *blkcg,
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blkg_get(blkg->parent);
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}
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ret = percpu_ref_init(&blkg->refcnt, blkg_release, 0,
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GFP_NOWAIT | __GFP_NOWARN);
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if (ret)
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goto err_cancel_ref;
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/* invoke per-policy init */
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for (i = 0; i < BLKCG_MAX_POLS; i++) {
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struct blkcg_policy *pol = blkcg_policy[i];
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@ -249,6 +284,8 @@ static struct blkcg_gq *blkg_create(struct blkcg *blkcg,
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blkg_put(blkg);
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return ERR_PTR(ret);
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err_cancel_ref:
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percpu_ref_exit(&blkg->refcnt);
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err_put_congested:
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wb_congested_put(wb_congested);
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err_put_css:
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@ -387,7 +424,7 @@ static void blkg_destroy(struct blkcg_gq *blkg)
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* Put the reference taken at the time of creation so that when all
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* queues are gone, group can be destroyed.
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*/
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blkg_put(blkg);
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percpu_ref_kill(&blkg->refcnt);
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}
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/**
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@ -414,29 +451,6 @@ static void blkg_destroy_all(struct request_queue *q)
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q->root_rl.blkg = NULL;
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}
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/*
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* A group is RCU protected, but having an rcu lock does not mean that one
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* can access all the fields of blkg and assume these are valid. For
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* example, don't try to follow throtl_data and request queue links.
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*
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* Having a reference to blkg under an rcu allows accesses to only values
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* local to groups like group stats and group rate limits.
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*/
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void __blkg_release_rcu(struct rcu_head *rcu_head)
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{
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struct blkcg_gq *blkg = container_of(rcu_head, struct blkcg_gq, rcu_head);
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/* release the blkcg and parent blkg refs this blkg has been holding */
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css_put(&blkg->blkcg->css);
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if (blkg->parent)
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blkg_put(blkg->parent);
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wb_congested_put(blkg->wb_congested);
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blkg_free(blkg);
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}
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EXPORT_SYMBOL_GPL(__blkg_release_rcu);
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/*
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* The next function used by blk_queue_for_each_rl(). It's a bit tricky
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* because the root blkg uses @q->root_rl instead of its own rl.
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@ -126,7 +126,7 @@ struct blkcg_gq {
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struct request_list rl;
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/* reference count */
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atomic_t refcnt;
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struct percpu_ref refcnt;
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/* is this blkg online? protected by both blkcg and q locks */
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bool online;
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@ -490,8 +490,7 @@ static inline int blkg_path(struct blkcg_gq *blkg, char *buf, int buflen)
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*/
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static inline void blkg_get(struct blkcg_gq *blkg)
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{
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WARN_ON_ONCE(atomic_read(&blkg->refcnt) <= 0);
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atomic_inc(&blkg->refcnt);
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percpu_ref_get(&blkg->refcnt);
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}
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/**
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@ -503,7 +502,7 @@ static inline void blkg_get(struct blkcg_gq *blkg)
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*/
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static inline struct blkcg_gq *blkg_try_get(struct blkcg_gq *blkg)
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{
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if (atomic_inc_not_zero(&blkg->refcnt))
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if (percpu_ref_tryget(&blkg->refcnt))
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return blkg;
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return NULL;
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}
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@ -517,23 +516,19 @@ static inline struct blkcg_gq *blkg_try_get(struct blkcg_gq *blkg)
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*/
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static inline struct blkcg_gq *blkg_try_get_closest(struct blkcg_gq *blkg)
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{
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while (!atomic_inc_not_zero(&blkg->refcnt))
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while (!percpu_ref_tryget(&blkg->refcnt))
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blkg = blkg->parent;
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return blkg;
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}
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void __blkg_release_rcu(struct rcu_head *rcu);
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/**
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* blkg_put - put a blkg reference
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* @blkg: blkg to put
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*/
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static inline void blkg_put(struct blkcg_gq *blkg)
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{
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WARN_ON_ONCE(atomic_read(&blkg->refcnt) <= 0);
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if (atomic_dec_and_test(&blkg->refcnt))
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call_rcu(&blkg->rcu_head, __blkg_release_rcu);
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percpu_ref_put(&blkg->refcnt);
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}
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/**
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