From ae11889636111199dbcf47283b4167f578b69472 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Tue, 18 Aug 2015 14:55:20 -0700 Subject: 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 Cc: Vivek Goyal Cc: Arianna Avanzini Signed-off-by: Jens Axboe --- block/cfq-iosched.c | 33 ++++++++++----------------------- 1 file changed, 10 insertions(+), 23 deletions(-) (limited to 'block/cfq-iosched.c') 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; -- cgit v1.2.3