blkcg: make blkcg_gq's hierarchical
Currently a child blkg (blkcg_gq) can be created even if its parent doesn't exist. ie. Given a blkg, it's not guaranteed that its ancestors will exist. This makes it difficult to implement proper hierarchy support for blkcg policies. Always create blkgs recursively and make a child blkg hold a reference to its parent. blkg->parent is added so that finding the parent is easy. blkcg_parent() is also added in the process. This change can be visible to userland. e.g. while issuing IO in a nested cgroup didn't affect the ancestors at all, now it will initialize all ancestor blkgs and zero stats for the request_queue will always appear on them. While this is userland visible, this shouldn't cause any functional difference. Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Vivek Goyal <vgoyal@redhat.com>
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93e6d5d8f5
Коммит
3c54786590
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@ -201,7 +201,16 @@ static struct blkcg_gq *blkg_create(struct blkcg *blkcg,
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}
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blkg = new_blkg;
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/* insert */
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/* link parent and insert */
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if (blkcg_parent(blkcg)) {
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blkg->parent = __blkg_lookup(blkcg_parent(blkcg), q, false);
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if (WARN_ON_ONCE(!blkg->parent)) {
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blkg = ERR_PTR(-EINVAL);
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goto err_put_css;
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}
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blkg_get(blkg->parent);
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}
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spin_lock(&blkcg->lock);
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ret = radix_tree_insert(&blkcg->blkg_tree, q->id, blkg);
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if (likely(!ret)) {
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@ -213,6 +222,10 @@ static struct blkcg_gq *blkg_create(struct blkcg *blkcg,
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if (!ret)
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return blkg;
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/* @blkg failed fully initialized, use the usual release path */
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blkg_put(blkg);
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return ERR_PTR(ret);
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err_put_css:
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css_put(&blkcg->css);
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err_free_blkg:
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@ -226,8 +239,9 @@ err_free_blkg:
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* @q: request_queue of interest
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*
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* Lookup blkg for the @blkcg - @q pair. If it doesn't exist, try to
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* create one. This function should be called under RCU read lock and
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* @q->queue_lock.
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* create one. blkg creation is performed recursively from blkcg_root such
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* that all non-root blkg's have access to the parent blkg. This function
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* should be called under RCU read lock and @q->queue_lock.
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*
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* Returns pointer to the looked up or created blkg on success, ERR_PTR()
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* value on error. If @q is dead, returns ERR_PTR(-EINVAL). If @q is not
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@ -252,7 +266,23 @@ struct blkcg_gq *blkg_lookup_create(struct blkcg *blkcg,
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if (blkg)
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return blkg;
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return blkg_create(blkcg, q, NULL);
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/*
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* Create blkgs walking down from blkcg_root to @blkcg, so that all
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* non-root blkgs have access to their parents.
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*/
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while (true) {
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struct blkcg *pos = blkcg;
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struct blkcg *parent = blkcg_parent(blkcg);
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while (parent && !__blkg_lookup(parent, q, false)) {
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pos = parent;
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parent = blkcg_parent(parent);
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}
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blkg = blkg_create(pos, q, NULL);
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if (pos == blkcg || IS_ERR(blkg))
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return blkg;
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}
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}
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EXPORT_SYMBOL_GPL(blkg_lookup_create);
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@ -321,8 +351,10 @@ static void blkg_rcu_free(struct rcu_head *rcu_head)
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void __blkg_release(struct blkcg_gq *blkg)
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{
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/* release the extra blkcg reference this blkg has been holding */
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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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/*
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* A group is freed in rcu manner. But having an rcu lock does not
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@ -94,8 +94,13 @@ struct blkcg_gq {
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struct list_head q_node;
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struct hlist_node blkcg_node;
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struct blkcg *blkcg;
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/* all non-root blkcg_gq's are guaranteed to have access to parent */
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struct blkcg_gq *parent;
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/* request allocation list for this blkcg-q pair */
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struct request_list rl;
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/* reference count */
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int refcnt;
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@ -180,6 +185,19 @@ static inline struct blkcg *bio_blkcg(struct bio *bio)
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return task_blkcg(current);
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}
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/**
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* blkcg_parent - get the parent of a blkcg
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* @blkcg: blkcg of interest
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*
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* Return the parent blkcg of @blkcg. Can be called anytime.
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*/
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static inline struct blkcg *blkcg_parent(struct blkcg *blkcg)
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{
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struct cgroup *pcg = blkcg->css.cgroup->parent;
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return pcg ? cgroup_to_blkcg(pcg) : NULL;
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}
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/**
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* blkg_to_pdata - get policy private data
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* @blkg: blkg of interest
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