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authorTejun Heo <tj@kernel.org>2015-08-19 00:55:20 +0300
committerJens Axboe <axboe@fb.com>2015-08-19 01:49:17 +0300
commitae11889636111199dbcf47283b4167f578b69472 (patch)
tree02870926926c7391d41e4b40a8b5bcf82ce34aab /block/cfq-iosched.c
parentc9589f03e490956628ff91a1da133216dc796b63 (diff)
downloadlinux-ae11889636111199dbcf47283b4167f578b69472.tar.xz
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>
Diffstat (limited to 'block/cfq-iosched.c')
-rw-r--r--block/cfq-iosched.c33
1 files changed, 10 insertions, 23 deletions
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index a4429b366820..0994f3b523a8 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -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;
-
- /* 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);
- }
+ struct blkcg_gq *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;