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Date: Mon, 17 Oct 2022 16:28:00 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: Dawei Li <set_pte_at@...look.com>, axboe@...nel.dk, tj@...nel.org,
paolo.valente@...aro.org
Cc: linux-block@...r.kernel.org, cgroups@...r.kernel.org,
linux-kernel@...r.kernel.org, "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH 2/2] block: Make refcnt of bfq_group/bfq_queue atomic
Hi,
在 2022/10/11 22:52, Dawei Li 写道:
> For most implementations of reference count, atomic_t is preferred
> for their natural-born atomic ops capability.
> Change the reference count of bfq_group/bfq_queue, both data structures
> and related ops, into atomic.
I'm afraid that this is unnecessary, the modifications of reference
count are inside spin_lock() in bfq.
Thanks,
Kuai
>
> Signed-off-by: Dawei Li <set_pte_at@...look.com>
> ---
> block/bfq-cgroup.c | 8 +++----
> block/bfq-iosched.c | 54 +++++++++++++++++++++++----------------------
> block/bfq-iosched.h | 6 ++---
> block/bfq-wf2q.c | 6 ++---
> 4 files changed, 37 insertions(+), 37 deletions(-)
>
> diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c
> index 144bca006463..714126ba21b6 100644
> --- a/block/bfq-cgroup.c
> +++ b/block/bfq-cgroup.c
> @@ -316,14 +316,12 @@ struct bfq_group *bfqq_group(struct bfq_queue *bfqq)
>
> static void bfqg_get(struct bfq_group *bfqg)
> {
> - bfqg->ref++;
> + atomic_inc(&bfqg->ref);
> }
>
> static void bfqg_put(struct bfq_group *bfqg)
> {
> - bfqg->ref--;
> -
> - if (bfqg->ref == 0)
> + if (atomic_dec_and_test(&bfqg->ref))
> kfree(bfqg);
> }
>
> @@ -659,7 +657,7 @@ void bfq_bfqq_move(struct bfq_data *bfqd, struct bfq_queue *bfqq,
> * Get extra reference to prevent bfqq from being freed in
> * next possible expire or deactivate.
> */
> - bfqq->ref++;
> + atomic_inc(&bfqq->ref);
>
> /* If bfqq is empty, then bfq_bfqq_expire also invokes
> * bfq_del_bfqq_busy, thereby removing bfqq and its entity
> diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
> index 7ea427817f7f..fbe5624be71f 100644
> --- a/block/bfq-iosched.c
> +++ b/block/bfq-iosched.c
> @@ -935,7 +935,7 @@ void bfq_weights_tree_add(struct bfq_data *bfqd, struct bfq_queue *bfqq,
>
> inc_counter:
> bfqq->weight_counter->num_active++;
> - bfqq->ref++;
> + atomic_inc(&bfqq->ref);
> }
>
> /*
> @@ -1224,9 +1224,10 @@ bfq_bfqq_resume_state(struct bfq_queue *bfqq, struct bfq_data *bfqd,
>
> static int bfqq_process_refs(struct bfq_queue *bfqq)
> {
> - return bfqq->ref - bfqq->entity.allocated -
> + return atomic_read(&bfqq->ref) - bfqq->entity.allocated -
> bfqq->entity.on_st_or_in_serv -
> - (bfqq->weight_counter != NULL) - bfqq->stable_ref;
> + (bfqq->weight_counter != NULL) -
> + atomic_read(&bfqq->stable_ref);
> }
>
> /* Empty burst list and add just bfqq (see comments on bfq_handle_burst) */
> @@ -2818,7 +2819,7 @@ bfq_setup_merge(struct bfq_queue *bfqq, struct bfq_queue *new_bfqq)
> * expected to be associated with new_bfqq as they happen to
> * issue I/O.
> */
> - new_bfqq->ref += process_refs;
> + atomic_add(process_refs, &new_bfqq->ref);
> return new_bfqq;
> }
>
> @@ -5255,10 +5256,10 @@ void bfq_put_queue(struct bfq_queue *bfqq)
> struct hlist_node *n;
> struct bfq_group *bfqg = bfqq_group(bfqq);
>
> - bfq_log_bfqq(bfqq->bfqd, bfqq, "put_queue: %p %d", bfqq, bfqq->ref);
> + bfq_log_bfqq(bfqq->bfqd, bfqq, "put_queue: %p %d", bfqq,
> + atomic_read(&bfqq->ref));
>
> - bfqq->ref--;
> - if (bfqq->ref)
> + if (!atomic_dec_and_test(&bfqq->ref))
> return;
>
> if (!hlist_unhashed(&bfqq->burst_list_node)) {
> @@ -5328,7 +5329,7 @@ void bfq_put_queue(struct bfq_queue *bfqq)
>
> static void bfq_put_stable_ref(struct bfq_queue *bfqq)
> {
> - bfqq->stable_ref--;
> + atomic_dec(&bfqq->stable_ref);
> bfq_put_queue(bfqq);
> }
>
> @@ -5358,7 +5359,7 @@ static void bfq_exit_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq)
> bfq_schedule_dispatch(bfqd);
> }
>
> - bfq_log_bfqq(bfqd, bfqq, "exit_bfqq: %p, %d", bfqq, bfqq->ref);
> + bfq_log_bfqq(bfqd, bfqq, "exit_bfqq: %p, %d", bfqq, atomic_read(&bfqq->ref));
>
> bfq_put_cooperator(bfqq);
>
> @@ -5507,7 +5508,7 @@ static void bfq_init_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq,
> INIT_HLIST_NODE(&bfqq->woken_list_node);
> INIT_HLIST_HEAD(&bfqq->woken_list);
>
> - bfqq->ref = 0;
> + atomic_set(&bfqq->ref, 0);
> bfqq->bfqd = bfqd;
>
> if (bic)
> @@ -5710,12 +5711,12 @@ static struct bfq_queue *bfq_do_or_sched_stable_merge(struct bfq_data *bfqd,
> * to prevent it from being freed,
> * until we decide whether to merge
> */
> - last_bfqq_created->ref++;
> + atomic_inc(&last_bfqq_created->ref);
> /*
> * need to keep track of stable refs, to
> * compute process refs correctly
> */
> - last_bfqq_created->stable_ref++;
> + atomic_inc(&last_bfqq_created->stable_ref);
> /*
> * Record the bfqq to merge to.
> */
> @@ -5767,20 +5768,21 @@ static struct bfq_queue *bfq_get_queue(struct bfq_data *bfqd,
> * prune it.
> */
> if (async_bfqq) {
> - bfqq->ref++; /*
> - * Extra group reference, w.r.t. sync
> - * queue. This extra reference is removed
> - * only if bfqq->bfqg disappears, to
> - * guarantee that this queue is not freed
> - * until its group goes away.
> - */
> + atomic_inc(&bfqq->ref);
> + /*
> + * Extra group reference, w.r.t. sync
> + * queue. This extra reference is removed
> + * only if bfqq->bfqg disappears, to
> + * guarantee that this queue is not freed
> + * until its group goes away.
> + */
> bfq_log_bfqq(bfqd, bfqq, "get_queue, bfqq not in async: %p, %d",
> - bfqq, bfqq->ref);
> + bfqq, atomic_read(&bfqq->ref));
> *async_bfqq = bfqq;
> }
>
> out:
> - bfqq->ref++; /* get a process reference to this queue */
> + atomic_inc(&bfqq->ref); /* get a process reference to this queue */
>
> if (bfqq != &bfqd->oom_bfqq && is_sync && !respawn)
> bfqq = bfq_do_or_sched_stable_merge(bfqd, bfqq, bic);
> @@ -6059,7 +6061,7 @@ static bool __bfq_insert_request(struct bfq_data *bfqd, struct request *rq)
> */
> bfqq_request_allocated(new_bfqq);
> bfqq_request_freed(bfqq);
> - new_bfqq->ref++;
> + atomic_inc(&new_bfqq->ref);
> /*
> * If the bic associated with the process
> * issuing this request still points to bfqq
> @@ -6803,10 +6805,10 @@ static struct bfq_queue *bfq_init_rq(struct request *rq)
> }
>
> bfqq_request_allocated(bfqq);
> - bfqq->ref++;
> + atomic_inc(&bfqq->ref);
> bic->requests++;
> bfq_log_bfqq(bfqd, bfqq, "get_request %p: bfqq %p, %d",
> - rq, bfqq, bfqq->ref);
> + rq, bfqq, atomic_read(&bfqq->ref));
>
> rq->elv.priv[0] = bic;
> rq->elv.priv[1] = bfqq;
> @@ -6939,7 +6941,7 @@ static void __bfq_put_async_bfqq(struct bfq_data *bfqd,
> bfq_bfqq_move(bfqd, bfqq, bfqd->root_group);
>
> bfq_log_bfqq(bfqd, bfqq, "put_async_bfqq: putting %p, %d",
> - bfqq, bfqq->ref);
> + bfqq, atomic_read(&bfqq->ref));
> bfq_put_queue(bfqq);
> *bfqq_ptr = NULL;
> }
> @@ -7092,7 +7094,7 @@ static int bfq_init_queue(struct request_queue *q, struct elevator_type *e)
> * will not attempt to free it.
> */
> bfq_init_bfqq(bfqd, &bfqd->oom_bfqq, NULL, 1, 0);
> - bfqd->oom_bfqq.ref++;
> + atomic_inc(&bfqd->oom_bfqq.ref);
> bfqd->oom_bfqq.new_ioprio = BFQ_DEFAULT_QUEUE_IOPRIO;
> bfqd->oom_bfqq.new_ioprio_class = IOPRIO_CLASS_BE;
> bfqd->oom_bfqq.entity.new_weight =
> diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h
> index 64ee618064ba..71ac0de80bb0 100644
> --- a/block/bfq-iosched.h
> +++ b/block/bfq-iosched.h
> @@ -234,9 +234,9 @@ struct bfq_ttime {
> */
> struct bfq_queue {
> /* reference counter */
> - int ref;
> + atomic_t ref;
> /* counter of references from other queues for delayed stable merge */
> - int stable_ref;
> + atomic_t stable_ref;
> /* parent bfq_data */
> struct bfq_data *bfqd;
>
> @@ -928,7 +928,7 @@ struct bfq_group {
> char blkg_path[128];
>
> /* reference counter (see comments in bfq_bic_update_cgroup) */
> - int ref;
> + atomic_t ref;
> /* Is bfq_group still online? */
> bool online;
>
> diff --git a/block/bfq-wf2q.c b/block/bfq-wf2q.c
> index 8fc3da4c23bb..60a9a2c1fc8d 100644
> --- a/block/bfq-wf2q.c
> +++ b/block/bfq-wf2q.c
> @@ -512,9 +512,9 @@ static void bfq_get_entity(struct bfq_entity *entity)
> struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);
>
> if (bfqq) {
> - bfqq->ref++;
> + atomic_inc(&bfqq->ref);
> bfq_log_bfqq(bfqq->bfqd, bfqq, "get_entity: %p %d",
> - bfqq, bfqq->ref);
> + bfqq, atomic_read(&bfqq->ref));
> }
> }
>
> @@ -1611,7 +1611,7 @@ bool __bfq_bfqd_reset_in_service(struct bfq_data *bfqd)
> * reference to the queue. If this is the case, then
> * bfqq gets freed here.
> */
> - int ref = in_serv_bfqq->ref;
> + int ref = atomic_read(&in_serv_bfqq->ref);
> bfq_put_queue(in_serv_bfqq);
> if (ref == 1)
> return true;
>
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