blkcg: consolidate blkg creation in blkcg_bio_issue_check()
blkg (blkcg_gq) currently is created by blkcg policies invoking
blkg_lookup_create() which ends up repeating about the same code in
different policies. Theoretically, this can avoid the overhead of
looking and/or creating blkg's if blkcg is enabled but no policy is in
use; however, the cost of blkg lookup / creation is very low
especially if only the root blkcg is in use which is highly likely if
no blkcg policy is in active use - it boils down to a single very
predictable conditional and surrounding RCU protection.
This patch consolidates blkg creation to a new function
blkcg_bio_issue_check() which is called during bio issue from
generic_make_request_checks(). blkcg_bio_issue_check() is now the
only function which tries to create missing blkg's. The subsequent
policy and request_list operations just perform blkg_lookup() and if
missing falls back to the root.
* blk_get_rl() no longer tries to create blkg. It uses blkg_lookup()
instead of blkg_lookup_create().
* blk_throtl_bio() is now called from blkcg_bio_issue_check() with rcu
read locked and blkg already looked up. Both throtl_lookup_tg() and
throtl_lookup_create_tg() are dropped.
* cfq is similarly updated. cfq_lookup_create_cfqg() is replaced with
cfq_lookup_cfqg()which uses blkg_lookup().
This consolidates blkg handling and avoids unnecessary blkg creation
retries under memory pressure. In addition, this provides a common
bio entry point into blkcg where things like common accounting can be
performed.
v2: Build fixes for !CONFIG_CFQ_GROUP_IOSCHED and
!CONFIG_BLK_DEV_THROTTLING.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Arianna Avanzini <avanzini.arianna@gmail.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h
index 0609bce..4d1659c 100644
--- a/include/linux/blk-cgroup.h
+++ b/include/linux/blk-cgroup.h
@@ -421,8 +421,8 @@
* or if either the blkcg or queue is going away. Fall back to
* root_rl in such cases.
*/
- blkg = blkg_lookup_create(blkcg, q);
- if (unlikely(IS_ERR(blkg)))
+ blkg = blkg_lookup(blkcg, q);
+ if (unlikely(!blkg))
goto root_rl;
blkg_get(blkg);
@@ -636,6 +636,39 @@
u64_stats_update_end(&to->syncp);
}
+#ifdef CONFIG_BLK_DEV_THROTTLING
+extern bool blk_throtl_bio(struct request_queue *q, struct blkcg_gq *blkg,
+ struct bio *bio);
+#else
+static inline bool blk_throtl_bio(struct request_queue *q, struct blkcg_gq *blkg,
+ struct bio *bio) { return false; }
+#endif
+
+static inline bool blkcg_bio_issue_check(struct request_queue *q,
+ struct bio *bio)
+{
+ struct blkcg *blkcg;
+ struct blkcg_gq *blkg;
+ bool throtl = false;
+
+ rcu_read_lock();
+ blkcg = bio_blkcg(bio);
+
+ blkg = blkg_lookup(blkcg, q);
+ if (unlikely(!blkg)) {
+ spin_lock_irq(q->queue_lock);
+ blkg = blkg_lookup_create(blkcg, q);
+ if (IS_ERR(blkg))
+ blkg = NULL;
+ spin_unlock_irq(q->queue_lock);
+ }
+
+ throtl = blk_throtl_bio(q, blkg, bio);
+
+ rcu_read_unlock();
+ return !throtl;
+}
+
#else /* CONFIG_BLK_CGROUP */
struct blkcg {
@@ -689,6 +722,9 @@
static inline void blk_rq_set_rl(struct request *rq, struct request_list *rl) { }
static inline struct request_list *blk_rq_rl(struct request *rq) { return &rq->q->root_rl; }
+static inline bool blkcg_bio_issue_check(struct request_queue *q,
+ struct bio *bio) { return true; }
+
#define blk_queue_for_each_rl(rl, q) \
for ((rl) = &(q)->root_rl; (rl); (rl) = NULL)