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blkcg: consolidate blkg creation in blkcg_bio_issue_check()

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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>
This commit is contained in:
Tejun Heo 2015-08-18 14:55:20 -07:00 committed by Jens Axboe
parent c9589f03e4
commit ae11889636
6 changed files with 57 additions and 99 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
block/blk-cgroup.c
View File

@ -153,6 +153,7 @@ struct blkcg_gq *blkg_lookup_slowpath(struct blkcg *blkcg,
return NULL;
}
EXPORT_SYMBOL_GPL(blkg_lookup_slowpath);
/*
* If @new_blkg is %NULL, this function tries to allocate a new one as
@ -295,7 +296,6 @@ struct blkcg_gq *blkg_lookup_create(struct blkcg *blkcg,
return blkg;
}
}
EXPORT_SYMBOL_GPL(blkg_lookup_create);
static void blkg_destroy(struct blkcg_gq *blkg)
{

4
block/blk-core.c
View File

@ -1889,8 +1889,8 @@ generic_make_request_checks(struct bio *bio)
*/
create_io_context(GFP_ATOMIC, q->node);
if (blk_throtl_bio(q, bio))
return false; /* throttled, will be resubmitted later */
if (!blkcg_bio_issue_check(q, bio))
return false;
trace_block_bio_queue(q, bio);
return true;

72
block/blk-throttle.c
View File

@ -182,11 +182,6 @@ static inline struct blkcg_gq *tg_to_blkg(struct throtl_grp *tg)
return pd_to_blkg(&tg->pd);
}
static inline struct throtl_grp *td_root_tg(struct throtl_data *td)
{
return blkg_to_tg(td->queue->root_blkg);
}
/**
* sq_to_tg - return the throl_grp the specified service queue belongs to
* @sq: the throtl_service_queue of interest
@ -449,39 +444,6 @@ static void throtl_pd_reset_stats(struct blkg_policy_data *pd)
}
}
static struct throtl_grp *throtl_lookup_tg(struct throtl_data *td,
struct blkcg *blkcg)
{
return blkg_to_tg(blkg_lookup(blkcg, td->queue));
}
static struct throtl_grp *throtl_lookup_create_tg(struct throtl_data *td,
struct blkcg *blkcg)
{
struct request_queue *q = td->queue;
struct throtl_grp *tg = NULL;
/*
* This is the common case when there are no blkcgs. Avoid lookup
* in this case
*/
if (blkcg == &blkcg_root) {
tg = td_root_tg(td);
} else {
struct blkcg_gq *blkg;
blkg = blkg_lookup_create(blkcg, q);
/* if %NULL and @q is alive, fall back to root_tg */
if (!IS_ERR(blkg))
tg = blkg_to_tg(blkg);
else
tg = td_root_tg(td);
}
return tg;
}
static struct throtl_grp *
throtl_rb_first(struct throtl_service_queue *parent_sq)
{
@ -1403,46 +1365,26 @@ static struct blkcg_policy blkcg_policy_throtl = {
.pd_reset_stats_fn = throtl_pd_reset_stats,
};
bool blk_throtl_bio(struct request_queue *q, struct bio *bio)
bool blk_throtl_bio(struct request_queue *q, struct blkcg_gq *blkg,
struct bio *bio)
{
struct throtl_data *td = q->td;
struct throtl_qnode *qn = NULL;
struct throtl_grp *tg;
struct throtl_grp *tg = blkg_to_tg(blkg ?: q->root_blkg);
struct throtl_service_queue *sq;
bool rw = bio_data_dir(bio);
struct blkcg *blkcg;
bool throttled = false;
WARN_ON_ONCE(!rcu_read_lock_held());
/* see throtl_charge_bio() */
if (bio->bi_rw & REQ_THROTTLED)
if ((bio->bi_rw & REQ_THROTTLED) || !tg->has_rules[rw])
goto out;
/*
* A throtl_grp pointer retrieved under rcu can be used to access
* basic fields like stats and io rates. If a group has no rules,
* just update the dispatch stats in lockless manner and return.
*/
rcu_read_lock();
blkcg = bio_blkcg(bio);
tg = throtl_lookup_tg(td, blkcg);
if (tg) {
if (!tg->has_rules[rw]) {
throtl_update_dispatch_stats(tg_to_blkg(tg),
bio->bi_iter.bi_size, bio->bi_rw);
goto out_unlock_rcu;
}
}
/*
* Either group has not been allocated yet or it is not an unlimited
* IO group
*/
spin_lock_irq(q->queue_lock);
if (unlikely(blk_queue_bypass(q)))
goto out_unlock;
tg = throtl_lookup_create_tg(td, blkcg);
sq = &tg->service_queue;
while (true) {
@ -1507,8 +1449,6 @@ bool blk_throtl_bio(struct request_queue *q, struct bio *bio)
out_unlock:
spin_unlock_irq(q->queue_lock);
out_unlock_rcu:
rcu_read_unlock();
out:
/*
* As multiple blk-throtls may stack in the same issue path, we

5
block/blk.h
View File

@ -266,15 +266,10 @@ static inline struct io_context *create_io_context(gfp_t gfp_mask, int node)
* Internal throttling interface
*/
#ifdef CONFIG_BLK_DEV_THROTTLING
extern bool blk_throtl_bio(struct request_queue *q, struct bio *bio);
extern void blk_throtl_drain(struct request_queue *q);
extern int blk_throtl_init(struct request_queue *q);
extern void blk_throtl_exit(struct request_queue *q);
#else /* CONFIG_BLK_DEV_THROTTLING */
static inline bool blk_throtl_bio(struct request_queue *q, struct bio *bio)
{
return false;
}
static inline void blk_throtl_drain(struct request_queue *q) { }
static inline int blk_throtl_init(struct request_queue *q) { return 0; }
static inline void blk_throtl_exit(struct request_queue *q) { }

33
block/cfq-iosched.c
View File

@ -1683,28 +1683,15 @@ static void cfq_pd_reset_stats(struct blkg_policy_data *pd)
cfqg_stats_reset(&cfqg->dead_stats);
}
/*
* Search for the cfq group current task belongs to. request_queue lock must
* be held.
*/
static struct cfq_group *cfq_lookup_create_cfqg(struct cfq_data *cfqd,
struct blkcg *blkcg)
static struct cfq_group *cfq_lookup_cfqg(struct cfq_data *cfqd,
struct blkcg *blkcg)
{
struct request_queue *q = cfqd->queue;
struct cfq_group *cfqg = NULL;
struct blkcg_gq *blkg;
/* avoid lookup for the common case where there's no blkcg */
if (blkcg == &blkcg_root) {
cfqg = cfqd->root_group;
} else {
struct blkcg_gq *blkg;
blkg = blkg_lookup_create(blkcg, q);
if (!IS_ERR(blkg))
cfqg = blkg_to_cfqg(blkg);
}
return cfqg;
blkg = blkg_lookup(blkcg, cfqd->queue);
if (likely(blkg))
return blkg_to_cfqg(blkg);
return NULL;
}
static void cfq_link_cfqq_cfqg(struct cfq_queue *cfqq, struct cfq_group *cfqg)
@ -2108,8 +2095,8 @@ static struct cftype cfq_blkcg_files[] = {
{ } /* terminate */
};
#else /* GROUP_IOSCHED */
static struct cfq_group *cfq_lookup_create_cfqg(struct cfq_data *cfqd,
struct blkcg *blkcg)
static struct cfq_group *cfq_lookup_cfqg(struct cfq_data *cfqd,
struct blkcg *blkcg)
{
return cfqd->root_group;
}
@ -3716,7 +3703,7 @@ cfq_get_queue(struct cfq_data *cfqd, bool is_sync, struct cfq_io_cq *cic,
struct cfq_group *cfqg;
rcu_read_lock();
cfqg = cfq_lookup_create_cfqg(cfqd, bio_blkcg(bio));
cfqg = cfq_lookup_cfqg(cfqd, bio_blkcg(bio));
if (!cfqg) {
cfqq = &cfqd->oom_cfqq;
goto out;

40
include/linux/blk-cgroup.h
View File

@ -421,8 +421,8 @@ static inline struct request_list *blk_get_rl(struct request_queue *q,
* 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 @@ static inline void blkg_rwstat_merge(struct blkg_rwstat *to,
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_put_rl(struct request_list *rl) { }
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)