[PATCH V4 7/7] loop: don't add worker into idle list

Ming Lei
2021-08-06T08:04:25Z

We can retrieve any workers via xarray, so not add it into idle list.
Meantime reduce .lo_work_lock coverage, especially we don't need that
in IO path except for adding/deleting worker into xarray.

Also replace .last_ran_at with .reclaim_time, which is set when adding
loop command into worker->cmd_list. Meantime reclaim the worker when
the worker is expired and no any pending commands.

Acked-by: Dan Schatzberg <schatzberg.dan@gmail.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
drivers/block/loop.c | 178 ++++++++++++++++++++++++++-----------------
1 file changed, 108 insertions(+), 70 deletions(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index f77fa9e5eb49..93a3350ac175 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -973,10 +973,11 @@ static void loop_config_discard(struct loop_device *lo)
struct loop_worker {
struct work_struct work;
struct list_head cmd_list;
- struct list_head idle_list;
struct loop_device *lo;
struct cgroup_subsys_state *blkcg_css;
- unsigned long last_ran_at;
+ unsigned long reclaim_time;
+ spinlock_t lock;
+ refcount_t refcnt;
};

static void loop_workfn(struct work_struct *work);
@@ -1024,63 +1025,95 @@ static struct cgroup_subsys_state *loop_rq_get_memcg_css(
return NULL;
}

-static void loop_queue_work(struct loop_device *lo, struct loop_cmd *cmd)
+static struct loop_worker *loop_alloc_or_get_worker(struct loop_device *lo,
+ struct cgroup_subsys_state *blkcg_css)
{
- struct loop_worker *worker = NULL;
- struct work_struct *work;
- struct list_head *cmd_list;
- struct cgroup_subsys_state *blkcg_css = loop_rq_blkcg_css(cmd);
gfp_t gfp = GFP_NOWAIT | __GFP_NOWARN;
+ struct loop_worker *worker = kzalloc(sizeof(*worker), gfp);
+ struct loop_worker *worker_old;

- spin_lock(&lo->lo_work_lock);
-
- if (queue_on_root_worker(blkcg_css))
- goto queue_work;
-
- /* css->id is unique in each cgroup subsystem */
- worker = xa_load(&lo->workers, loop_blkcg_css_id(blkcg_css));
- if (worker)
- goto queue_work;
-
- worker = kzalloc(sizeof(*worker), gfp);
- /*
- * In the event we cannot allocate a worker, just queue on the
- * rootcg worker and issue the I/O as the rootcg
- */
if (!worker)
- goto queue_work;
+ return NULL;

worker->blkcg_css = blkcg_css;
- css_get(worker->blkcg_css);
INIT_WORK(&worker->work, loop_workfn);
INIT_LIST_HEAD(&worker->cmd_list);
- INIT_LIST_HEAD(&worker->idle_list);
worker->lo = lo;
+ spin_lock_init(&worker->lock);
+ refcount_set(&worker->refcnt, 2); /* INIT + INC */

- if (xa_err(xa_store(&lo->workers, loop_blkcg_css_id(blkcg_css),
- worker, gfp))) {
+ spin_lock(&lo->lo_work_lock);
+ /* maybe someone is storing a new worker */
+ worker_old = xa_load(&lo->workers, loop_blkcg_css_id(blkcg_css));
+ if (!worker_old || !refcount_inc_not_zero(&worker_old->refcnt)) {
+ if (xa_err(xa_store(&lo->workers,
+ loop_blkcg_css_id(blkcg_css),
+ worker, gfp))) {
+ kfree(worker);
+ worker = NULL;
+ } else {
+ if (!work_pending(&lo->idle_work.work))
+ schedule_delayed_work(&lo->idle_work,
+ LOOP_IDLE_WORKER_TIMEOUT);
+ css_get(worker->blkcg_css);
+ }
+ } else {
kfree(worker);
- worker = NULL;
+ worker = worker_old;
}
+ spin_unlock(&lo->lo_work_lock);

-queue_work:
- if (worker) {
+ return worker;
+}
+
+static void loop_release_worker(struct loop_worker *worker)
+{
+ css_put(worker->blkcg_css);
+ kfree_rcu(worker);
+}
+
+static void loop_queue_work(struct loop_device *lo, struct loop_cmd *cmd)
+{
+ struct loop_worker *worker = NULL;
+ struct work_struct *work;
+ struct list_head *cmd_list;
+ struct cgroup_subsys_state *blkcg_css = loop_rq_blkcg_css(cmd);
+ spinlock_t *lock;
+
+ if (!queue_on_root_worker(blkcg_css)) {
+ int ret = 0;
+
+ rcu_read_lock();
+ /* css->id is unique in each cgroup subsystem */
+ worker = xa_load(&lo->workers, loop_blkcg_css_id(blkcg_css));
+ if (worker)
+ ret = refcount_inc_not_zero(&worker->refcnt);
+ rcu_read_unlock();
+
+ if (!worker || !ret)
+ worker = loop_alloc_or_get_worker(lo, blkcg_css);
/*
- * We need to remove from the idle list here while
- * holding the lock so that the idle timer doesn't
- * free the worker
+ * In the event we cannot allocate a worker, just queue on the
+ * rootcg worker and issue the I/O as the rootcg
*/
- if (!list_empty(&worker->idle_list))
- list_del_init(&worker->idle_list);
+ }
+
+ if (worker) {
work = &worker->work;
cmd_list = &worker->cmd_list;
+ lock = &worker->lock;
} else {
work = &lo->rootcg_work;
cmd_list = &lo->rootcg_cmd_list;
+ lock = &lo->lo_work_lock;
}
+
+ spin_lock(lock);
list_add_tail(&cmd->list_entry, cmd_list);
+ if (worker)
+ worker->reclaim_time = jiffies + LOOP_IDLE_WORKER_TIMEOUT;
+ spin_unlock(lock);
queue_work(lo->workqueue, work);
- spin_unlock(&lo->lo_work_lock);
}

static void loop_update_rotational(struct loop_device *lo)
@@ -1202,28 +1235,39 @@ loop_set_status_from_info(struct loop_device *lo,
return 0;
}

-static void loop_set_timer(struct loop_device *lo)
+static bool loop_need_reclaim_worker(struct loop_worker *worker)
{
- schedule_delayed_work(&lo->idle_work, LOOP_IDLE_WORKER_TIMEOUT);
+ bool reclaim;
+
+ spin_lock(&worker->lock);
+ if (list_empty(&worker->cmd_list) &&
+ time_is_before_jiffies(worker->reclaim_time))
+ reclaim = true;
+ else
+ reclaim = false;
+ spin_unlock(&worker->lock);
+
+ return reclaim;
}

static void __loop_free_idle_workers(struct loop_device *lo, bool force)
{
- struct loop_worker *pos, *worker;
+ struct loop_worker *worker;
+ unsigned long id;

spin_lock(&lo->lo_work_lock);
- list_for_each_entry_safe(worker, pos, &lo->idle_worker_list,
- idle_list) {
- if (!force && time_is_after_jiffies(worker->last_ran_at +
- LOOP_IDLE_WORKER_TIMEOUT))
- break;
- list_del(&worker->idle_list);
- xa_erase(&lo->workers, loop_blkcg_css_id(worker->blkcg_css));
- css_put(worker->blkcg_css);
- kfree(worker);
- }
- if (!list_empty(&lo->idle_worker_list))
- loop_set_timer(lo);
+ xa_for_each(&lo->workers, id, worker) {
+ if (!force && !loop_need_reclaim_worker(worker))
+ continue;
+
+ xa_erase(&worker->lo->workers,
+ loop_blkcg_css_id(worker->blkcg_css));
+ if (refcount_dec_and_test(&worker->refcnt))
+ loop_release_worker(worker);
+ }
+ if (!xa_empty(&lo->workers))
+ schedule_delayed_work(&lo->idle_work,
+ LOOP_IDLE_WORKER_TIMEOUT);
spin_unlock(&lo->lo_work_lock);
}

@@ -2235,42 +2279,36 @@ static void loop_handle_cmd(struct loop_cmd *cmd)
}

static void loop_process_work(struct loop_worker *worker,
- struct list_head *cmd_list, struct loop_device *lo)
+ struct list_head *cmd_list, spinlock_t *lock)
{
int orig_flags = current->flags;
struct loop_cmd *cmd;
LIST_HEAD(list);
+ int cnt = 0;

current->flags |= PF_LOCAL_THROTTLE | PF_MEMALLOC_NOIO;

- spin_lock(&lo->lo_work_lock);
+ spin_lock(lock);
again:
list_splice_init(cmd_list, &list);
- spin_unlock(&lo->lo_work_lock);
+ spin_unlock(lock);

while (!list_empty(&list)) {
cmd = list_first_entry(&list, struct loop_cmd, list_entry);
list_del_init(&cmd->list_entry);

loop_handle_cmd(cmd);
+ cnt++;
}

- spin_lock(&lo->lo_work_lock);
+ spin_lock(lock);
if (!list_empty(cmd_list))
goto again;
-
- /*
- * We only add to the idle list if there are no pending cmds
- * *and* the worker will not run again which ensures that it
- * is safe to free any worker on the idle list
- */
- if (worker && !work_pending(&worker->work)) {
- worker->last_ran_at = jiffies;
- list_add_tail(&worker->idle_list, &lo->idle_worker_list);
- loop_set_timer(lo);
- }
- spin_unlock(&lo->lo_work_lock);
+ spin_unlock(lock);
current->flags = orig_flags;
+
+ if (worker && refcount_sub_and_test(cnt, &worker->refcnt))
+ loop_release_worker(worker);
}

static void loop_workfn(struct work_struct *work)
@@ -2285,11 +2323,11 @@ static void loop_workfn(struct work_struct *work)
if (memcg_css) {
old_memcg = set_active_memcg(
mem_cgroup_from_css(memcg_css));
- loop_process_work(worker, &worker->cmd_list, worker->lo);
+ loop_process_work(worker, &worker->cmd_list, &worker->lock);
set_active_memcg(old_memcg);
css_put(memcg_css);
} else {
- loop_process_work(worker, &worker->cmd_list, worker->lo);
+ loop_process_work(worker, &worker->cmd_list, &worker->lock);
}
kthread_associate_blkcg(NULL);
}
@@ -2298,7 +2336,7 @@ static void loop_rootcg_workfn(struct work_struct *work)
{
struct loop_device *lo =
container_of(work, struct loop_device, rootcg_work);
- loop_process_work(NULL, &lo->rootcg_cmd_list, lo);
+ loop_process_work(NULL, &lo->rootcg_cmd_list, &lo->lo_work_lock);
}

static const struct blk_mq_ops loop_mq_ops = {
--
2.31.1