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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
Download Patch File Download Diff File Expand all files Collapse all files

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;