[PATCH 03/11] blkcg: make root blkcg allocation use %GFP_KERNEL

Tejun Heo
2012-04-26T22:02:41Z

Currently, blkcg_activate_policy() depends on %GFP_ATOMIC allocation
from __blkg_lookup_create() for root blkcg creation. This could make
policy fail unnecessarily.

Make blkg_alloc() take @gfp_mask, __blkg_lookup_create() take an
optional @new_blkg for preallocated blkg, and blkcg_activate_policy()
preload radix tree and preallocate blkg with %GFP_KERNEL before trying
to create the root blkg.

Signed-off-by: Tejun Heo <tj@kernel.org>
---
block/blk-cgroup.c | 58 +++++++++++++++++++++++++++++++++++++--------------
1 files changed, 42 insertions(+), 16 deletions(-)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 197fb50..a8f2f03 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -91,16 +91,18 @@ static void blkg_free(struct blkcg_gq *blkg)
* blkg_alloc - allocate a blkg
* @blkcg: block cgroup the new blkg is associated with
* @q: request_queue the new blkg is associated with
+ * @gfp_mask: allocation mask to use
*
* Allocate a new blkg assocating @blkcg and @q.
*/
-static struct blkcg_gq *blkg_alloc(struct blkcg *blkcg, struct request_queue *q)
+static struct blkcg_gq *blkg_alloc(struct blkcg *blkcg, struct request_queue *q,
+ gfp_t gfp_mask)
{
struct blkcg_gq *blkg;
int i;

/* alloc and init base part */
- blkg = kzalloc_node(sizeof(*blkg), GFP_ATOMIC, q->node);
+ blkg = kzalloc_node(sizeof(*blkg), gfp_mask, q->node);
if (!blkg)
return NULL;

@@ -117,7 +119,7 @@ static struct blkcg_gq *blkg_alloc(struct blkcg *blkcg, struct request_queue *q)
continue;

/* alloc per-policy data and attach it to blkg */
- pd = kzalloc_node(pol->pd_size, GFP_ATOMIC, q->node);
+ pd = kzalloc_node(pol->pd_size, gfp_mask, q->node);
if (!pd) {
blkg_free(blkg);
return NULL;
@@ -175,8 +177,13 @@ struct blkcg_gq *blkg_lookup(struct blkcg *blkcg, struct request_queue *q)
}
EXPORT_SYMBOL_GPL(blkg_lookup);

+/*
+ * If @new_blkg is %NULL, this function tries to allocate a new one as
+ * necessary using %GFP_ATOMIC. @new_blkg is always consumed on return.
+ */
static struct blkcg_gq *__blkg_lookup_create(struct blkcg *blkcg,
- struct request_queue *q)
+ struct request_queue *q,
+ struct blkcg_gq *new_blkg)
{
struct blkcg_gq *blkg;
bool preloaded;
@@ -189,18 +196,23 @@ static struct blkcg_gq *__blkg_lookup_create(struct blkcg *blkcg,
blkg = __blkg_lookup(blkcg, q);
if (blkg) {
rcu_assign_pointer(blkcg->blkg_hint, blkg);
- return blkg;
+ goto out_free;
}

/* blkg holds a reference to blkcg */
- if (!css_tryget(&blkcg->css))
- return ERR_PTR(-EINVAL);
+ if (!css_tryget(&blkcg->css)) {
+ blkg = ERR_PTR(-EINVAL);
+ goto out_free;
+ }

/* allocate */
- ret = -ENOMEM;
- blkg = blkg_alloc(blkcg, q);
- if (unlikely(!blkg))
- goto err_put;
+ if (!new_blkg) {
+ ret = -ENOMEM;
+ new_blkg = blkg_alloc(blkcg, q, GFP_ATOMIC);
+ if (unlikely(!new_blkg))
+ goto out_put;
+ }
+ blkg = new_blkg;

/* insert */
preloaded = !radix_tree_preload(GFP_ATOMIC);
@@ -217,10 +229,13 @@ static struct blkcg_gq *__blkg_lookup_create(struct blkcg *blkcg,
radix_tree_preload_end();
if (!ret)
return blkg;
-err_put:
+
+ blkg = ERR_PTR(ret);
+out_put:
css_put(&blkcg->css);
- blkg_free(blkg);
- return ERR_PTR(ret);
+out_free:
+ blkg_free(new_blkg);
+ return blkg;
}

struct blkcg_gq *blkg_lookup_create(struct blkcg *blkcg,
@@ -232,7 +247,7 @@ struct blkcg_gq *blkg_lookup_create(struct blkcg *blkcg,
*/
if (unlikely(blk_queue_bypass(q)))
return ERR_PTR(blk_queue_dead(q) ? -EINVAL : -EBUSY);
- return __blkg_lookup_create(blkcg, q);
+ return __blkg_lookup_create(blkcg, q, NULL);
}
EXPORT_SYMBOL_GPL(blkg_lookup_create);

@@ -732,19 +747,30 @@ int blkcg_activate_policy(struct request_queue *q,
struct blkcg_gq *blkg;
struct blkg_policy_data *pd, *n;
int cnt = 0, ret;
+ bool preloaded;

if (blkcg_policy_enabled(q, pol))
return 0;

+ /* preallocations for root blkg */
+ blkg = blkg_alloc(&blkcg_root, q, GFP_KERNEL);
+ if (!blkg)
+ return -ENOMEM;
+
+ preloaded = !radix_tree_preload(GFP_KERNEL);
+
blk_queue_bypass_start(q);

/* make sure the root blkg exists and count the existing blkgs */
spin_lock_irq(q->queue_lock);

rcu_read_lock();
- blkg = __blkg_lookup_create(&blkcg_root, q);
+ blkg = __blkg_lookup_create(&blkcg_root, q, blkg);
rcu_read_unlock();

+ if (preloaded)
+ radix_tree_preload_end();
+
if (IS_ERR(blkg)) {
ret = PTR_ERR(blkg);
goto out_unlock;
--
1.7.7.3