Re: [PATCH 2/2] block: Make refcnt of bfq_group/bfq_queue atomic

From: Yu Kuai
Date: Mon Oct 17 2022 - 04:30:27 EST

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@xxxxxxxxxxx>
---
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;