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Mon, 24 Feb 2020 14:18:07 -0800 (PST) Received: from dschatzberg-fedora-PC0Y6AEN.thefacebook.com ([2620:10d:c091:500::2:b19b]) by smtp.gmail.com with ESMTPSA id o17sm6648870qtj.80.2020.02.24.14.18.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 24 Feb 2020 14:18:07 -0800 (PST) From: Dan Schatzberg To: Cc: Dan Schatzberg , Jens Axboe , Tejun Heo , Li Zefan , Johannes Weiner , Michal Hocko , Vladimir Davydov , Andrew Morton , Hugh Dickins , Roman Gushchin , Shakeel Butt , Chris Down , Yang Shi , Thomas Gleixner , linux-block@vger.kernel.org (open list:BLOCK LAYER), linux-kernel@vger.kernel.org (open list), cgroups@vger.kernel.org (open list:CONTROL GROUP (CGROUP)), linux-mm@kvack.org (open list:CONTROL GROUP - MEMORY RESOURCE CONTROLLER (MEMCG)) Subject: [PATCH v3 1/3] loop: Use worker per cgroup instead of kworker Date: Mon, 24 Feb 2020 17:17:45 -0500 Message-Id: X-Mailer: git-send-email 2.21.1 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Existing uses of loop device may have multiple cgroups reading/writing to the same device. Simply charging resources for I/O to the backing file could result in priority inversion where one cgroup gets synchronously blocked, holding up all other I/O to the loop device. In order to avoid this priority inversion, we use a single workqueue where each work item is a "struct loop_worker" which contains a queue of struct loop_cmds to issue. The loop device maintains a tree mapping blk css_id -> loop_worker. This allows each cgroup to independently make forward progress issuing I/O to the backing file. There is also a single queue for I/O associated with the rootcg which can be used in cases of extreme memory shortage where we cannot allocate a loop_worker. The locking for the tree and queues is fairly heavy handed - we acquire the per-loop-device spinlock any time either is accessed. The existing implementation serializes all I/O through a single thread anyways, so I don't believe this is any worse. Signed-off-by: Dan Schatzberg Acked-by: Johannes Weiner --- drivers/block/loop.c | 207 +++++++++++++++++++++++++++++++++++++------ drivers/block/loop.h | 11 ++- 2 files changed, 188 insertions(+), 30 deletions(-) diff --git a/drivers/block/loop.c b/drivers/block/loop.c index 739b372a5112..a9b05cacc393 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -70,7 +70,6 @@ #include #include #include -#include #include #include #include @@ -83,6 +82,8 @@ =20 #include =20 +#define LOOP_IDLE_WORKER_TIMEOUT (60 * HZ) + static DEFINE_IDR(loop_index_idr); static DEFINE_MUTEX(loop_ctl_mutex); =20 @@ -891,27 +892,100 @@ static void loop_config_discard(struct loop_device= *lo) =20 static void loop_unprepare_queue(struct loop_device *lo) { - kthread_flush_worker(&lo->worker); - kthread_stop(lo->worker_task); -} - -static int loop_kthread_worker_fn(void *worker_ptr) -{ - current->flags |=3D PF_LESS_THROTTLE | PF_MEMALLOC_NOIO; - return kthread_worker_fn(worker_ptr); + destroy_workqueue(lo->workqueue); } =20 static int loop_prepare_queue(struct loop_device *lo) { - kthread_init_worker(&lo->worker); - lo->worker_task =3D kthread_run(loop_kthread_worker_fn, - &lo->worker, "loop%d", lo->lo_number); - if (IS_ERR(lo->worker_task)) + lo->workqueue =3D alloc_workqueue("loop%d", + WQ_UNBOUND | WQ_FREEZABLE | + WQ_MEM_RECLAIM, + lo->lo_number); + if (IS_ERR(lo->workqueue)) return -ENOMEM; - set_user_nice(lo->worker_task, MIN_NICE); + return 0; } =20 +struct loop_worker { + struct rb_node rb_node; + struct work_struct work; + struct list_head cmd_list; + struct list_head idle_list; + struct loop_device *lo; + struct cgroup_subsys_state *css; + unsigned long last_ran_at; +}; + +static void loop_workfn(struct work_struct *work); +static void loop_rootcg_workfn(struct work_struct *work); +static void loop_free_idle_workers(struct timer_list *timer); + +static void loop_queue_work(struct loop_device *lo, struct loop_cmd *cmd= ) +{ + struct rb_node **node =3D &(lo->worker_tree.rb_node), *parent =3D NULL; + struct loop_worker *cur_worker, *worker =3D NULL; + struct work_struct *work; + struct list_head *cmd_list; + + spin_lock_irq(&lo->lo_lock); + + if (!cmd->css) + goto queue_work; + + node =3D &lo->worker_tree.rb_node; + + while (*node) { + parent =3D *node; + cur_worker =3D container_of(*node, struct loop_worker, rb_node); + if (cur_worker->css =3D=3D cmd->css) { + worker =3D cur_worker; + break; + } else if ((long)cur_worker->css < (long)cmd->css) { + node =3D &(*node)->rb_left; + } else { + node =3D &(*node)->rb_right; + } + } + if (worker) + goto queue_work; + + worker =3D kzalloc(sizeof(struct loop_worker), GFP_NOWAIT | __GFP_NOWAR= N); + /* + * In the event we cannot allocate a worker, just queue on the + * rootcg worker + */ + if (!worker) + goto queue_work; + + worker->css =3D cmd->css; + css_get(worker->css); + INIT_WORK(&worker->work, loop_workfn); + INIT_LIST_HEAD(&worker->cmd_list); + INIT_LIST_HEAD(&worker->idle_list); + worker->lo =3D lo; + rb_link_node(&worker->rb_node, parent, node); + rb_insert_color(&worker->rb_node, &lo->worker_tree); +queue_work: + if (worker) { + /* + * We need to remove from the idle list here while + * holding the lock so that the idle timer doesn't + * free the worker + */ + if (!list_empty(&worker->idle_list)) + list_del_init(&worker->idle_list); + work =3D &worker->work; + cmd_list =3D &worker->cmd_list; + } else { + work =3D &lo->rootcg_work; + cmd_list =3D &lo->rootcg_cmd_list; + } + list_add_tail(&cmd->list_entry, cmd_list); + queue_work(lo->workqueue, work); + spin_unlock_irq(&lo->lo_lock); +} + static void loop_update_rotational(struct loop_device *lo) { struct file *file =3D lo->lo_backing_file; @@ -993,6 +1067,12 @@ static int loop_set_fd(struct loop_device *lo, fmod= e_t mode, =20 set_device_ro(bdev, (lo_flags & LO_FLAGS_READ_ONLY) !=3D 0); =20 + INIT_WORK(&lo->rootcg_work, loop_rootcg_workfn); + INIT_LIST_HEAD(&lo->rootcg_cmd_list); + INIT_LIST_HEAD(&lo->idle_worker_list); + lo->worker_tree =3D RB_ROOT; + timer_setup(&lo->timer, loop_free_idle_workers, + TIMER_DEFERRABLE); lo->use_dio =3D false; lo->lo_device =3D bdev; lo->lo_flags =3D lo_flags; @@ -1101,6 +1181,7 @@ static int __loop_clr_fd(struct loop_device *lo, bo= ol release) int err =3D 0; bool partscan =3D false; int lo_number; + struct loop_worker *pos, *worker; =20 mutex_lock(&loop_ctl_mutex); if (WARN_ON_ONCE(lo->lo_state !=3D Lo_rundown)) { @@ -1117,9 +1198,28 @@ static int __loop_clr_fd(struct loop_device *lo, b= ool release) /* freeze request queue during the transition */ blk_mq_freeze_queue(lo->lo_queue); =20 + /* + * Ordering here is a bit tricky: + * + * 1) flush/destroy workqueue without lock held so outstanding + * I/O is issued and all active workers go idle + * + * 2) Grab lock, free all idle workers + * + * 3) unlock, del_timer_sync so if timer raced it will be a no-op + */ + loop_unprepare_queue(lo); spin_lock_irq(&lo->lo_lock); lo->lo_backing_file =3D NULL; + list_for_each_entry_safe(worker, pos, &lo->idle_worker_list, + idle_list) { + list_del(&worker->idle_list); + rb_erase(&worker->rb_node, &lo->worker_tree); + css_put(worker->css); + kfree(worker); + } spin_unlock_irq(&lo->lo_lock); + del_timer_sync(&lo->timer); =20 loop_release_xfer(lo); lo->transfer =3D NULL; @@ -1154,7 +1254,6 @@ static int __loop_clr_fd(struct loop_device *lo, bo= ol release) =20 partscan =3D lo->lo_flags & LO_FLAGS_PARTSCAN && bdev; lo_number =3D lo->lo_number; - loop_unprepare_queue(lo); out_unlock: mutex_unlock(&loop_ctl_mutex); if (partscan) { @@ -1932,7 +2031,7 @@ static blk_status_t loop_queue_rq(struct blk_mq_hw_= ctx *hctx, } else #endif cmd->css =3D NULL; - kthread_queue_work(&lo->worker, &cmd->work); + loop_queue_work(lo, cmd); =20 return BLK_STS_OK; } @@ -1958,26 +2057,82 @@ static void loop_handle_cmd(struct loop_cmd *cmd) } } =20 -static void loop_queue_work(struct kthread_work *work) +static void loop_set_timer(struct loop_device *lo) +{ + timer_reduce(&lo->timer, jiffies + LOOP_IDLE_WORKER_TIMEOUT); +} + +static void loop_process_work(struct loop_worker *worker, + struct list_head *cmd_list, struct loop_device *lo) { - struct loop_cmd *cmd =3D - container_of(work, struct loop_cmd, work); + int orig_flags =3D current->flags; + struct loop_cmd *cmd; =20 - loop_handle_cmd(cmd); + current->flags |=3D PF_LESS_THROTTLE | PF_MEMALLOC_NOIO; + spin_lock_irq(&lo->lo_lock); + while (!list_empty(cmd_list)) { + cmd =3D container_of( + cmd_list->next, struct loop_cmd, list_entry); + list_del(cmd_list->next); + spin_unlock_irq(&lo->lo_lock); + + loop_handle_cmd(cmd); + cond_resched(); + + spin_lock_irq(&lo->lo_lock); + } + + /* + * 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 =3D jiffies; + list_add_tail(&worker->idle_list, &lo->idle_worker_list); + loop_set_timer(lo); + } + spin_unlock_irq(&lo->lo_lock); + current->flags =3D orig_flags; } =20 -static int loop_init_request(struct blk_mq_tag_set *set, struct request = *rq, - unsigned int hctx_idx, unsigned int numa_node) +static void loop_workfn(struct work_struct *work) { - struct loop_cmd *cmd =3D blk_mq_rq_to_pdu(rq); + struct loop_worker *worker =3D + container_of(work, struct loop_worker, work); + loop_process_work(worker, &worker->cmd_list, worker->lo); +} =20 - kthread_init_work(&cmd->work, loop_queue_work); - return 0; +static void loop_rootcg_workfn(struct work_struct *work) +{ + struct loop_device *lo =3D + container_of(work, struct loop_device, rootcg_work); + loop_process_work(NULL, &lo->rootcg_cmd_list, lo); +} + +static void loop_free_idle_workers(struct timer_list *timer) +{ + struct loop_device *lo =3D container_of(timer, struct loop_device, time= r); + struct loop_worker *pos, *worker; + + spin_lock_irq(&lo->lo_lock); + list_for_each_entry_safe(worker, pos, &lo->idle_worker_list, + idle_list) { + if (time_is_after_jiffies(worker->last_ran_at + + LOOP_IDLE_WORKER_TIMEOUT)) + break; + list_del(&worker->idle_list); + rb_erase(&worker->rb_node, &lo->worker_tree); + css_put(worker->css); + kfree(worker); + } + if (!list_empty(&lo->idle_worker_list)) + loop_set_timer(lo); + spin_unlock_irq(&lo->lo_lock); } =20 static const struct blk_mq_ops loop_mq_ops =3D { .queue_rq =3D loop_queue_rq, - .init_request =3D loop_init_request, .complete =3D lo_complete_rq, }; =20 diff --git a/drivers/block/loop.h b/drivers/block/loop.h index af75a5ee4094..87fd0e372227 100644 --- a/drivers/block/loop.h +++ b/drivers/block/loop.h @@ -14,7 +14,6 @@ #include #include #include -#include #include =20 /* Possible states of device */ @@ -54,8 +53,12 @@ struct loop_device { =20 spinlock_t lo_lock; int lo_state; - struct kthread_worker worker; - struct task_struct *worker_task; + struct workqueue_struct *workqueue; + struct work_struct rootcg_work; + struct list_head rootcg_cmd_list; + struct list_head idle_worker_list; + struct rb_root worker_tree; + struct timer_list timer; bool use_dio; bool sysfs_inited; =20 @@ -65,7 +68,7 @@ struct loop_device { }; =20 struct loop_cmd { - struct kthread_work work; + struct list_head list_entry; bool use_aio; /* use AIO interface to handle I/O */ atomic_t ref; /* only for aio */ long ret; --=20 2.17.1