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Thu, 28 May 2020 06:55:15 -0700 (PDT) Received: from dschatzberg-fedora-PC0Y6AEN.thefacebook.com ([2620:10d:c091:480::1:1cb7]) by smtp.gmail.com with ESMTPSA id l186sm4890889qkf.89.2020.05.28.06.55.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 28 May 2020 06:55:14 -0700 (PDT) From: Dan Schatzberg To: Cc: Dan Schatzberg , Jens Axboe , Alexander Viro , Jan Kara , Amir Goldstein , Tejun Heo , Li Zefan , Johannes Weiner , Michal Hocko , Vladimir Davydov , Andrew Morton , Hugh Dickins , Roman Gushchin , Shakeel Butt , Chris Down , Yang Shi , Thomas Gleixner , Ingo Molnar , "Peter Zijlstra (Intel)" , Mathieu Desnoyers , Andrea Arcangeli , linux-block@vger.kernel.org (open list:BLOCK LAYER), linux-kernel@vger.kernel.org (open list), linux-fsdevel@vger.kernel.org (open list:FILESYSTEMS (VFS and infrastructure)), cgroups@vger.kernel.org (open list:CONTROL GROUP (CGROUP)), linux-mm@kvack.org (open list:CONTROL GROUP - MEMORY RESOURCE CONTROLLER (MEMCG)) Subject: [PATCH 1/4] loop: Use worker per cgroup instead of kworker Date: Thu, 28 May 2020 09:54:36 -0400 Message-Id: <20200528135444.11508-2-schatzberg.dan@gmail.com> X-Mailer: git-send-email 2.21.3 In-Reply-To: <20200528135444.11508-1-schatzberg.dan@gmail.com> References: <20200528135444.11508-1-schatzberg.dan@gmail.com> MIME-Version: 1.0 X-Rspamd-Queue-Id: 8C16010F97 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam05 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 a 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 --- drivers/block/loop.c | 203 ++++++++++++++++++++++++++++++++++++------- drivers/block/loop.h | 12 ++- 2 files changed, 178 insertions(+), 37 deletions(-) diff --git a/drivers/block/loop.c b/drivers/block/loop.c index da693e6a834e..378a68e5ccf3 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 @@ #include +#define LOOP_IDLE_WORKER_TIMEOUT (60 * HZ) + static DEFINE_IDR(loop_index_idr); static DEFINE_MUTEX(loop_ctl_mutex); @@ -911,27 +912,83 @@ static void loop_config_discard(struct loop_device *lo) blk_queue_flag_clear(QUEUE_FLAG_DISCARD, q); } -static void loop_unprepare_queue(struct loop_device *lo) -{ - kthread_flush_worker(&lo->worker); - kthread_stop(lo->worker_task); -} +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 int loop_kthread_worker_fn(void *worker_ptr) -{ - current->flags |= PF_LESS_THROTTLE | PF_MEMALLOC_NOIO; - return kthread_worker_fn(worker_ptr); -} +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 int loop_prepare_queue(struct loop_device *lo) +static void loop_queue_work(struct loop_device *lo, struct loop_cmd *cmd) { - kthread_init_worker(&lo->worker); - lo->worker_task = kthread_run(loop_kthread_worker_fn, - &lo->worker, "loop%d", lo->lo_number); - if (IS_ERR(lo->worker_task)) - return -ENOMEM; - set_user_nice(lo->worker_task, MIN_NICE); - return 0; + struct rb_node **node = &(lo->worker_tree.rb_node), *parent = NULL; + struct loop_worker *cur_worker, *worker = NULL; + struct work_struct *work; + struct list_head *cmd_list; + + spin_lock_irq(&lo->lo_work_lock); + + if (!cmd->css) + goto queue_work; + + node = &lo->worker_tree.rb_node; + + while (*node) { + parent = *node; + cur_worker = container_of(*node, struct loop_worker, rb_node); + if (cur_worker->css == cmd->css) { + worker = cur_worker; + break; + } else if ((long)cur_worker->css < (long)cmd->css) { + node = &(*node)->rb_left; + } else { + node = &(*node)->rb_right; + } + } + if (worker) + goto queue_work; + + worker = kzalloc(sizeof(struct loop_worker), GFP_NOWAIT | __GFP_NOWARN); + /* + * In the event we cannot allocate a worker, just queue on the + * rootcg worker + */ + if (!worker) + goto queue_work; + + worker->css = 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 = 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 = &worker->work; + cmd_list = &worker->cmd_list; + } else { + work = &lo->rootcg_work; + cmd_list = &lo->rootcg_cmd_list; + } + list_add_tail(&cmd->list_entry, cmd_list); + queue_work(lo->workqueue, work); + spin_unlock_irq(&lo->lo_work_lock); } static void loop_update_rotational(struct loop_device *lo) @@ -1007,14 +1064,25 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode, size = get_loop_size(lo, file); if ((loff_t)(sector_t)size != size) goto out_unlock; - error = loop_prepare_queue(lo); - if (error) + lo->workqueue = alloc_workqueue("loop%d", + WQ_UNBOUND | WQ_FREEZABLE | + WQ_MEM_RECLAIM, + lo->lo_number); + if (!lo->workqueue) { + error = -ENOMEM; goto out_unlock; + } error = 0; set_device_ro(bdev, (lo_flags & LO_FLAGS_READ_ONLY) != 0); + 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 = RB_ROOT; + timer_setup(&lo->timer, loop_free_idle_workers, + TIMER_DEFERRABLE); lo->use_dio = false; lo->lo_device = bdev; lo->lo_flags = lo_flags; @@ -1123,6 +1191,7 @@ static int __loop_clr_fd(struct loop_device *lo, bool release) int err = 0; bool partscan = false; int lo_number; + struct loop_worker *pos, *worker; mutex_lock(&loop_ctl_mutex); if (WARN_ON_ONCE(lo->lo_state != Lo_rundown)) { @@ -1139,6 +1208,18 @@ static int __loop_clr_fd(struct loop_device *lo, bool release) /* freeze request queue during the transition */ blk_mq_freeze_queue(lo->lo_queue); + destroy_workqueue(lo->workqueue); + spin_lock_irq(&lo->lo_work_lock); + 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_work_lock); + del_timer_sync(&lo->timer); + spin_lock_irq(&lo->lo_lock); lo->lo_backing_file = NULL; spin_unlock_irq(&lo->lo_lock); @@ -1176,7 +1257,6 @@ static int __loop_clr_fd(struct loop_device *lo, bool release) partscan = lo->lo_flags & LO_FLAGS_PARTSCAN && bdev; lo_number = lo->lo_number; - loop_unprepare_queue(lo); out_unlock: mutex_unlock(&loop_ctl_mutex); if (partscan) { @@ -1954,7 +2034,7 @@ static blk_status_t loop_queue_rq(struct blk_mq_hw_ctx *hctx, } else #endif cmd->css = NULL; - kthread_queue_work(&lo->worker, &cmd->work); + loop_queue_work(lo, cmd); return BLK_STS_OK; } @@ -1983,26 +2063,82 @@ static void loop_handle_cmd(struct loop_cmd *cmd) } } -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) +{ + int orig_flags = current->flags; + struct loop_cmd *cmd; + + current->flags |= PF_LESS_THROTTLE | PF_MEMALLOC_NOIO; + spin_lock_irq(&lo->lo_work_lock); + while (!list_empty(cmd_list)) { + cmd = container_of( + cmd_list->next, struct loop_cmd, list_entry); + list_del(cmd_list->next); + spin_unlock_irq(&lo->lo_work_lock); + + loop_handle_cmd(cmd); + cond_resched(); + + spin_lock_irq(&lo->lo_work_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 = jiffies; + list_add_tail(&worker->idle_list, &lo->idle_worker_list); + loop_set_timer(lo); + } + spin_unlock_irq(&lo->lo_work_lock); + current->flags = orig_flags; +} + +static void loop_workfn(struct work_struct *work) { - struct loop_cmd *cmd = - container_of(work, struct loop_cmd, work); + struct loop_worker *worker = + container_of(work, struct loop_worker, work); + loop_process_work(worker, &worker->cmd_list, worker->lo); +} - loop_handle_cmd(cmd); +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); } -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_free_idle_workers(struct timer_list *timer) { - struct loop_cmd *cmd = blk_mq_rq_to_pdu(rq); + struct loop_device *lo = container_of(timer, struct loop_device, timer); + struct loop_worker *pos, *worker; - kthread_init_work(&cmd->work, loop_queue_work); - return 0; + spin_lock_irq(&lo->lo_work_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_work_lock); } static const struct blk_mq_ops loop_mq_ops = { .queue_rq = loop_queue_rq, - .init_request = loop_init_request, .complete = lo_complete_rq, }; @@ -2090,6 +2226,7 @@ static int loop_add(struct loop_device **l, int i) atomic_set(&lo->lo_refcnt, 0); lo->lo_number = i; spin_lock_init(&lo->lo_lock); + spin_lock_init(&lo->lo_work_lock); disk->major = LOOP_MAJOR; disk->first_minor = i << part_shift; disk->fops = &lo_fops; diff --git a/drivers/block/loop.h b/drivers/block/loop.h index af75a5ee4094..0162b55a68e1 100644 --- a/drivers/block/loop.h +++ b/drivers/block/loop.h @@ -14,7 +14,6 @@ #include #include #include -#include #include /* Possible states of device */ @@ -54,8 +53,13 @@ struct loop_device { spinlock_t lo_lock; int lo_state; - struct kthread_worker worker; - struct task_struct *worker_task; + spinlock_t lo_work_lock; + 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; @@ -65,7 +69,7 @@ struct loop_device { }; 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;