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Commit 3c547865 authored by Tejun Heo's avatar Tejun Heo
Browse files

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: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarVivek Goyal <vgoyal@redhat.com>
parent 93e6d5d8

block/blk-cgroup.c

+37 −5
Original line number Diff line number Diff line
@@ -201,7 +201,16 @@ static struct blkcg_gq *blkg_create(struct blkcg *blkcg, 
	}

	blkg = new_blkg;



	/* insert */

	/* link parent and insert */

	if (blkcg_parent(blkcg)) {

		blkg->parent = __blkg_lookup(blkcg_parent(blkcg), q, false);

		if (WARN_ON_ONCE(!blkg->parent)) {

			blkg = ERR_PTR(-EINVAL);

			goto err_put_css;

		}

		blkg_get(blkg->parent);

	}



	spin_lock(&blkcg->lock);

	ret = radix_tree_insert(&blkcg->blkg_tree, q->id, blkg);

	if (likely(!ret)) {
@@ -213,6 +222,10 @@ static struct blkcg_gq *blkg_create(struct blkcg *blkcg, 
	if (!ret)

		return blkg;



	/* @blkg failed fully initialized, use the usual release path */

	blkg_put(blkg);

	return ERR_PTR(ret);



err_put_css:

	css_put(&blkcg->css);

err_free_blkg:
@@ -226,8 +239,9 @@ static struct blkcg_gq *blkg_create(struct blkcg *blkcg, 
 * @q: request_queue of interest

 *

 * Lookup blkg for the @blkcg - @q pair.  If it doesn't exist, try to

 * create one.  This function should be called under RCU read lock and

 * @q->queue_lock.

 * create one.  blkg creation is performed recursively from blkcg_root such

 * that all non-root blkg's have access to the parent blkg.  This function

 * should be called under RCU read lock and @q->queue_lock.

 *

 * Returns pointer to the looked up or created blkg on success, ERR_PTR()

 * value on error.  If @q is dead, returns ERR_PTR(-EINVAL).  If @q is not
@@ -252,7 +266,23 @@ struct blkcg_gq *blkg_lookup_create(struct blkcg *blkcg, 
	if (blkg)

		return blkg;



	return blkg_create(blkcg, q, NULL);

	/*

	 * Create blkgs walking down from blkcg_root to @blkcg, so that all

	 * non-root blkgs have access to their parents.

	 */

	while (true) {

		struct blkcg *pos = blkcg;

		struct blkcg *parent = blkcg_parent(blkcg);



		while (parent && !__blkg_lookup(parent, q, false)) {

			pos = parent;

			parent = blkcg_parent(parent);

		}



		blkg = blkg_create(pos, q, NULL);

		if (pos == blkcg || IS_ERR(blkg))

			return blkg;

	}

}

EXPORT_SYMBOL_GPL(blkg_lookup_create);
@@ -321,8 +351,10 @@ static void blkg_rcu_free(struct rcu_head *rcu_head) 


void __blkg_release(struct blkcg_gq *blkg)

{

	/* release the extra blkcg reference this blkg has been holding */

	/* release the blkcg and parent blkg refs this blkg has been holding */

	css_put(&blkg->blkcg->css);

	if (blkg->parent)

		blkg_put(blkg->parent);



	/*

	 * A group is freed in rcu manner. But having an rcu lock does not

block/blk-cgroup.h

+18 −0
Original line number Diff line number Diff line
@@ -94,8 +94,13 @@ struct blkcg_gq { 
	struct list_head		q_node;

	struct hlist_node		blkcg_node;

	struct blkcg			*blkcg;



	/* all non-root blkcg_gq's are guaranteed to have access to parent */

	struct blkcg_gq			*parent;



	/* request allocation list for this blkcg-q pair */

	struct request_list		rl;



	/* reference count */

	int				refcnt;
@@ -180,6 +185,19 @@ static inline struct blkcg *bio_blkcg(struct bio *bio) 
	return task_blkcg(current);

}



/**

 * blkcg_parent - get the parent of a blkcg

 * @blkcg: blkcg of interest

 *

 * Return the parent blkcg of @blkcg.  Can be called anytime.

 */

static inline struct blkcg *blkcg_parent(struct blkcg *blkcg)

{

	struct cgroup *pcg = blkcg->css.cgroup->parent;



	return pcg ? cgroup_to_blkcg(pcg) : NULL;

}



/**

 * blkg_to_pdata - get policy private data

 * @blkg: blkg of interest