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Message-Id: <1355524885-22719-5-git-send-email-tj@kernel.org>
Date: Fri, 14 Dec 2012 14:41:17 -0800
From: Tejun Heo <tj@...nel.org>
To: lizefan@...wei.com, axboe@...nel.dk, vgoyal@...hat.com
Cc: containers@...ts.linux-foundation.org, cgroups@...r.kernel.org,
linux-kernel@...r.kernel.org, ctalbott@...gle.com, rni@...gle.com,
Tejun Heo <tj@...nel.org>
Subject: [PATCH 04/12] 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@...nel.org>
---
block/blk-cgroup.c | 42 +++++++++++++++++++++++++++++++++++++-----
block/blk-cgroup.h | 18 ++++++++++++++++++
2 files changed, 55 insertions(+), 5 deletions(-)
diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index fde2286..c858628 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -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 @@ err_free_blkg:
* @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
diff --git a/block/blk-cgroup.h b/block/blk-cgroup.h
index 2459730..b26ed58 100644
--- a/block/blk-cgroup.h
+++ b/block/blk-cgroup.h
@@ -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;
@@ -181,6 +186,19 @@ static inline struct blkcg *bio_blkcg(struct bio *bio)
}
/**
+ * 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
* @pol: policy of interest
--
1.7.11.7
--
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