From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tejun Heo Subject: [PATCH 2/7] blkcg: use percpu_ref for blkcg_gq->refcnt Date: Sun, 12 Nov 2017 14:26:08 -0800 Message-ID: <20171112222613.3613362-3-tj@kernel.org> References: <20171112222613.3613362-1-tj@kernel.org> Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:from:to:cc:subject:date:message-id:in-reply-to:references; bh=cNMQKbAid5zR2IKMAop1rOwJqioXk2V055pYuJvIfRw=; b=oWZ9bMHl/yeZAOpGRLwHI/FdIb2W1NCnyG39E17BscGi8Ctdd/04YZEMQDpkzAwLxY PL7V5dw9r+TMeqsqPzkoZ6qgoRcOiTc9MMrSQzqT1Demg4FOzQwCez1Jtli82UZRmdN6 377bUSMZwe0Ugys+KTPJuZAcrWVzu+Q/O5E9i2Y6pH1mMdKx/0rBXVlFEPiqFjaEIdEf eVb2L+E6J8yc6D6056ShkhAWO8VKjhpaeDFZCOja2KRSUebksPLgXAuHoNUZAq4MFGcQ E5JycAciOtgK/MObn3M1zn9EinogzWvOdRC7lM88zJbBtMgWr5P7SQPeC748Y5++s0AB OhlQ== In-Reply-To: <20171112222613.3613362-1-tj@kernel.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: axboe@kernel.dk Cc: shli@kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com, lizefan@huawei.com, hannes@cmpxchg.org, cgroups@vger.kernel.org, guro@fb.com, Tejun Heo blkcg_gq->refcnt is an atomic_t. This was due to the following two reasons. * When blkcg_gq was added, the percpu memory allocator didn't support allocations from !GFP_KERNEL contexts. Because blkcg_gq's are created from IO issue paths, it couldn't use GFP_KERNEL allocations. * A blkcg_gq represents the connection between a cgroup and a request_queue. Because a in-flight bio already pins both, blkcg_gq didn't usually need explicit pinning, making the use of atomic_t acceptable albeit restrictive and fragile. Now that the percpu allocator supports !GFP_KERNEL allocations, there's no reason to keep using atomic_t refcnt. This will allow clean separation between bio and request layers helping blkcg support in blk-mq. Signed-off-by: Tejun Heo --- block/blk-cgroup.c | 21 ++++++++++++++++----- include/linux/blk-cgroup.h | 13 ++++--------- 2 files changed, 20 insertions(+), 14 deletions(-) diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c index 6482be5..60a4486 100644 --- a/block/blk-cgroup.c +++ b/block/blk-cgroup.c @@ -78,6 +78,7 @@ static void blkg_free(struct blkcg_gq *blkg) blkg_rwstat_exit(&blkg->stat_ios); blkg_rwstat_exit(&blkg->stat_bytes); + percpu_ref_exit(&blkg->refcnt); kfree(blkg); } @@ -89,7 +90,7 @@ static void blkg_free(struct blkcg_gq *blkg) * Having a reference to blkg under an rcu allows accesses to only values * local to groups like group stats and group rate limits. */ -void __blkg_release_rcu(struct rcu_head *rcu_head) +static void blkg_release_rcu(struct rcu_head *rcu_head) { struct blkcg_gq *blkg = container_of(rcu_head, struct blkcg_gq, rcu_head); @@ -102,7 +103,13 @@ void __blkg_release_rcu(struct rcu_head *rcu_head) blkg_free(blkg); } -EXPORT_SYMBOL_GPL(__blkg_release_rcu); + +static void blkg_release(struct percpu_ref *refcnt) +{ + struct blkcg_gq *blkg = container_of(refcnt, struct blkcg_gq, refcnt); + + call_rcu(&blkg->rcu_head, blkg_release_rcu); +} /** * blkg_alloc - allocate a blkg @@ -123,6 +130,11 @@ static struct blkcg_gq *blkg_alloc(struct blkcg *blkcg, struct request_queue *q, if (!blkg) return NULL; + if (percpu_ref_init(&blkg->refcnt, blkg_release, 0, gfp_mask)) { + kfree(blkg); + return NULL; + } + if (blkg_rwstat_init(&blkg->stat_bytes, gfp_mask) || blkg_rwstat_init(&blkg->stat_ios, gfp_mask)) goto err_free; @@ -130,7 +142,6 @@ static struct blkcg_gq *blkg_alloc(struct blkcg *blkcg, struct request_queue *q, blkg->q = q; INIT_LIST_HEAD(&blkg->q_node); blkg->blkcg = blkcg; - atomic_set(&blkg->refcnt, 1); /* root blkg uses @q->root_rl, init rl only for !root blkgs */ if (blkcg != &blkcg_root) { @@ -266,7 +277,7 @@ static struct blkcg_gq *blkg_create(struct blkcg *blkcg, return blkg; /* @blkg failed fully initialized, use the usual release path */ - blkg_put(blkg); + percpu_ref_kill(&blkg->refcnt); return ERR_PTR(ret); err_put_congested: @@ -373,7 +384,7 @@ static void blkg_destroy(struct blkcg_gq *blkg) * Put the reference taken at the time of creation so that when all * queues are gone, group can be destroyed. */ - blkg_put(blkg); + percpu_ref_kill(&blkg->refcnt); } /** diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h index 8bbc371..c0d4736 100644 --- a/include/linux/blk-cgroup.h +++ b/include/linux/blk-cgroup.h @@ -19,7 +19,7 @@ #include #include #include -#include +#include /* percpu_counter batch for blkg_[rw]stats, per-cpu drift doesn't matter */ #define BLKG_STAT_CPU_BATCH (INT_MAX / 2) @@ -123,7 +123,7 @@ struct blkcg_gq { struct request_list rl; /* reference count */ - atomic_t refcnt; + struct percpu_ref refcnt; /* is this blkg online? protected by both blkcg and q locks */ bool online; @@ -355,21 +355,16 @@ static inline int blkg_path(struct blkcg_gq *blkg, char *buf, int buflen) */ static inline void blkg_get(struct blkcg_gq *blkg) { - WARN_ON_ONCE(atomic_read(&blkg->refcnt) <= 0); - atomic_inc(&blkg->refcnt); + percpu_ref_get(&blkg->refcnt); } -void __blkg_release_rcu(struct rcu_head *rcu); - /** * blkg_put - put a blkg reference * @blkg: blkg to put */ static inline void blkg_put(struct blkcg_gq *blkg) { - WARN_ON_ONCE(atomic_read(&blkg->refcnt) <= 0); - if (atomic_dec_and_test(&blkg->refcnt)) - call_rcu(&blkg->rcu_head, __blkg_release_rcu); + percpu_ref_put(&blkg->refcnt); } /** -- 2.9.5