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blkcg: make root blkcg allocation use %GFP_KERNEL

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.

v2: __blkg_lookup_create() was returning %NULL on blkg alloc failure
   instead of ERR_PTR() value.  Fixed.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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htejun authored and axboe committed Jun 5, 2012
1 parent 1358986 commit 159749937a3e1605068a454b1607cdc5714f16e6
Showing with 43 additions and 16 deletions.
  1. +43 −16 block/blk-cgroup.c
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@@ -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;
int ret;
@@ -188,18 +195,24 @@ 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) {
+ new_blkg = blkg_alloc(blkcg, q, GFP_ATOMIC);
+ if (unlikely(!new_blkg)) {
+ blkg = ERR_PTR(-ENOMEM);
+ goto out_put;
+ }
+ }
+ blkg = new_blkg;
/* insert */
spin_lock(&blkcg->lock);
@@ -212,10 +225,13 @@ static struct blkcg_gq *__blkg_lookup_create(struct blkcg *blkcg,
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,
@@ -227,7 +243,7 @@ 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);
@@ -726,19 +742,30 @@ 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;

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