blkcg: factor out blkio_group creation
Currently both blk-throttle and cfq-iosched implement their own
blkio_group creation code in throtl_get_tg() and cfq_get_cfqg(). This
patch factors out the common code into blkg_lookup_create(), which
returns ERR_PTR value so that transitional failures due to queue
bypass can be distinguished from other failures.
* New plkio_policy_ops methods blkio_alloc_group_fn() and
blkio_link_group_fn added. Both are transitional and will be
removed once the blkg management code is fully moved into
blk-cgroup.c.
* blkio_alloc_group_fn() allocates policy-specific blkg which is
usually a larger data structure with blkg as the first entry and
intiailizes it. Note that initialization of blkg proper, including
percpu stats, is responsibility of blk-cgroup proper.
Note that default config (weight, bps...) initialization is done
from this method; otherwise, we end up violating locking order
between blkcg and q locks via blkcg_get_CONF() functions.
* blkio_link_group_fn() is called under queue_lock and responsible for
linking the blkg to the queue. blkcg side is handled by blk-cgroup
proper.
* The common blkg creation function is named blkg_lookup_create() and
blkiocg_lookup_group() is renamed to blkg_lookup() for consistency.
Also, throtl / cfq related functions are similarly [re]named for
consistency.
This simplifies blkcg policy implementations and enables further
cleanup.
-v2: Vivek noticed that blkg_lookup_create() incorrectly tested
blk_queue_dead() instead of blk_queue_bypass() leading a user of
the function ending up creating a new blkg on bypassing queue.
This is a bug introduced while relocating bypass patches before
this one. Fixed.
-v3: ERR_PTR patch folded into this one. @for_root added to
blkg_lookup_create() to allow creating root group on a bypassed
queue during elevator switch.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index aeeb798..2ae637b 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -181,17 +181,25 @@
call_rcu(&tg->rcu_head, throtl_free_tg);
}
-static void throtl_init_group(struct throtl_grp *tg)
+static struct blkio_group *throtl_alloc_blkio_group(struct request_queue *q,
+ struct blkio_cgroup *blkcg)
{
+ struct throtl_grp *tg;
+
+ tg = kzalloc_node(sizeof(*tg), GFP_ATOMIC, q->node);
+ if (!tg)
+ return NULL;
+
INIT_HLIST_NODE(&tg->tg_node);
RB_CLEAR_NODE(&tg->rb_node);
bio_list_init(&tg->bio_lists[0]);
bio_list_init(&tg->bio_lists[1]);
tg->limits_changed = false;
- /* Practically unlimited BW */
- tg->bps[0] = tg->bps[1] = -1;
- tg->iops[0] = tg->iops[1] = -1;
+ tg->bps[READ] = blkcg_get_read_bps(blkcg, tg->blkg.dev);
+ tg->bps[WRITE] = blkcg_get_write_bps(blkcg, tg->blkg.dev);
+ tg->iops[READ] = blkcg_get_read_iops(blkcg, tg->blkg.dev);
+ tg->iops[WRITE] = blkcg_get_write_iops(blkcg, tg->blkg.dev);
/*
* Take the initial reference that will be released on destroy
@@ -200,14 +208,8 @@
* exit or cgroup deletion path depending on who is exiting first.
*/
atomic_set(&tg->ref, 1);
-}
-/* Should be called with rcu read lock held (needed for blkcg) */
-static void
-throtl_add_group_to_td_list(struct throtl_data *td, struct throtl_grp *tg)
-{
- hlist_add_head(&tg->tg_node, &td->tg_list);
- td->nr_undestroyed_grps++;
+ return &tg->blkg;
}
static void
@@ -246,119 +248,62 @@
spin_unlock_irq(td->queue->queue_lock);
}
-static void throtl_init_add_tg_lists(struct throtl_data *td,
- struct throtl_grp *tg, struct blkio_cgroup *blkcg)
+static void throtl_link_blkio_group(struct request_queue *q,
+ struct blkio_group *blkg)
{
+ struct throtl_data *td = q->td;
+ struct throtl_grp *tg = tg_of_blkg(blkg);
+
__throtl_tg_fill_dev_details(td, tg);
- /* Add group onto cgroup list */
- blkiocg_add_blkio_group(blkcg, &tg->blkg, td->queue,
- tg->blkg.dev, BLKIO_POLICY_THROTL);
-
- tg->bps[READ] = blkcg_get_read_bps(blkcg, tg->blkg.dev);
- tg->bps[WRITE] = blkcg_get_write_bps(blkcg, tg->blkg.dev);
- tg->iops[READ] = blkcg_get_read_iops(blkcg, tg->blkg.dev);
- tg->iops[WRITE] = blkcg_get_write_iops(blkcg, tg->blkg.dev);
-
- throtl_add_group_to_td_list(td, tg);
-}
-
-/* Should be called without queue lock and outside of rcu period */
-static struct throtl_grp *throtl_alloc_tg(struct throtl_data *td)
-{
- struct throtl_grp *tg = NULL;
- int ret;
-
- tg = kzalloc_node(sizeof(*tg), GFP_ATOMIC, td->queue->node);
- if (!tg)
- return NULL;
-
- ret = blkio_alloc_blkg_stats(&tg->blkg);
-
- if (ret) {
- kfree(tg);
- return NULL;
- }
-
- throtl_init_group(tg);
- return tg;
+ hlist_add_head(&tg->tg_node, &td->tg_list);
+ td->nr_undestroyed_grps++;
}
static struct
-throtl_grp *throtl_find_tg(struct throtl_data *td, struct blkio_cgroup *blkcg)
+throtl_grp *throtl_lookup_tg(struct throtl_data *td, struct blkio_cgroup *blkcg)
{
struct throtl_grp *tg = NULL;
/*
* This is the common case when there are no blkio cgroups.
- * Avoid lookup in this case
- */
+ * Avoid lookup in this case
+ */
if (blkcg == &blkio_root_cgroup)
tg = td->root_tg;
else
- tg = tg_of_blkg(blkiocg_lookup_group(blkcg, td->queue,
- BLKIO_POLICY_THROTL));
+ tg = tg_of_blkg(blkg_lookup(blkcg, td->queue,
+ BLKIO_POLICY_THROTL));
__throtl_tg_fill_dev_details(td, tg);
return tg;
}
-static struct throtl_grp *throtl_get_tg(struct throtl_data *td,
- struct blkio_cgroup *blkcg)
+static struct throtl_grp *throtl_lookup_create_tg(struct throtl_data *td,
+ struct blkio_cgroup *blkcg)
{
- struct throtl_grp *tg = NULL, *__tg = NULL;
struct request_queue *q = td->queue;
-
- /* no throttling for dead queue */
- if (unlikely(blk_queue_bypass(q)))
- return NULL;
-
- tg = throtl_find_tg(td, blkcg);
- if (tg)
- return tg;
-
- if (!css_tryget(&blkcg->css))
- return NULL;
+ struct throtl_grp *tg = NULL;
/*
- * Need to allocate a group. Allocation of group also needs allocation
- * of per cpu stats which in-turn takes a mutex() and can block. Hence
- * we need to drop rcu lock and queue_lock before we call alloc.
+ * This is the common case when there are no blkio cgroups.
+ * Avoid lookup in this case
*/
- spin_unlock_irq(q->queue_lock);
- rcu_read_unlock();
-
- tg = throtl_alloc_tg(td);
-
- /* Group allocated and queue is still alive. take the lock */
- rcu_read_lock();
- spin_lock_irq(q->queue_lock);
- css_put(&blkcg->css);
-
- /* Make sure @q is still alive */
- if (unlikely(blk_queue_bypass(q))) {
- kfree(tg);
- return NULL;
- }
-
- /*
- * If some other thread already allocated the group while we were
- * not holding queue lock, free up the group
- */
- __tg = throtl_find_tg(td, blkcg);
-
- if (__tg) {
- kfree(tg);
- return __tg;
- }
-
- /* Group allocation failed. Account the IO to root group */
- if (!tg) {
+ if (blkcg == &blkio_root_cgroup) {
tg = td->root_tg;
- return tg;
+ } else {
+ struct blkio_group *blkg;
+
+ blkg = blkg_lookup_create(blkcg, q, BLKIO_POLICY_THROTL, false);
+
+ /* if %NULL and @q is alive, fall back to root_tg */
+ if (!IS_ERR(blkg))
+ tg = tg_of_blkg(blkg);
+ else if (!blk_queue_dead(q))
+ tg = td->root_tg;
}
- throtl_init_add_tg_lists(td, tg, blkcg);
+ __throtl_tg_fill_dev_details(td, tg);
return tg;
}
@@ -1107,6 +1052,8 @@
static struct blkio_policy_type blkio_policy_throtl = {
.ops = {
+ .blkio_alloc_group_fn = throtl_alloc_blkio_group,
+ .blkio_link_group_fn = throtl_link_blkio_group,
.blkio_unlink_group_fn = throtl_unlink_blkio_group,
.blkio_clear_queue_fn = throtl_clear_queue,
.blkio_update_group_read_bps_fn =
@@ -1141,7 +1088,7 @@
*/
rcu_read_lock();
blkcg = task_blkio_cgroup(current);
- tg = throtl_find_tg(td, blkcg);
+ tg = throtl_lookup_tg(td, blkcg);
if (tg) {
throtl_tg_fill_dev_details(td, tg);
@@ -1157,7 +1104,7 @@
* IO group
*/
spin_lock_irq(q->queue_lock);
- tg = throtl_get_tg(td, blkcg);
+ tg = throtl_lookup_create_tg(td, blkcg);
if (unlikely(!tg))
goto out_unlock;
@@ -1252,6 +1199,7 @@
int blk_throtl_init(struct request_queue *q)
{
struct throtl_data *td;
+ struct blkio_group *blkg;
td = kzalloc_node(sizeof(*td), GFP_KERNEL, q->node);
if (!td)
@@ -1262,13 +1210,17 @@
td->limits_changed = false;
INIT_DELAYED_WORK(&td->throtl_work, blk_throtl_work);
- /* alloc and Init root group. */
+ q->td = td;
td->queue = q;
+ /* alloc and init root group. */
rcu_read_lock();
spin_lock_irq(q->queue_lock);
- td->root_tg = throtl_get_tg(td, &blkio_root_cgroup);
+ blkg = blkg_lookup_create(&blkio_root_cgroup, q, BLKIO_POLICY_THROTL,
+ true);
+ if (!IS_ERR(blkg))
+ td->root_tg = tg_of_blkg(blkg);
spin_unlock_irq(q->queue_lock);
rcu_read_unlock();
@@ -1277,9 +1229,6 @@
kfree(td);
return -ENOMEM;
}
-
- /* Attach throtl data to request queue */
- q->td = td;
return 0;
}