From patchwork Thu Feb 20 16:51:51 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Dan Schatzberg X-Patchwork-Id: 11394611 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 05F21159A for ; Thu, 20 Feb 2020 16:52:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C5E05208E4 for ; Thu, 20 Feb 2020 16:52:39 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="mRplJTIV" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728354AbgBTQwg (ORCPT ); Thu, 20 Feb 2020 11:52:36 -0500 Received: from mail-qk1-f194.google.com ([209.85.222.194]:46726 "EHLO mail-qk1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727709AbgBTQwg (ORCPT ); Thu, 20 Feb 2020 11:52:36 -0500 Received: by mail-qk1-f194.google.com with SMTP id u124so4154305qkh.13; Thu, 20 Feb 2020 08:52:35 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=FYNVHlKgDQ46X+XbR/60sAiRfHp1T0eWqZr2l7PitAY=; b=mRplJTIVJvwxpfcqw1dz1JBHO/xQGnQyFaChntDSc5MNme2JxeChi/bpTJQGi2EMq1 8cIt6V0A0cRKVgMt8j34VVrEuLKAhSrGC593vKSouczGi3i55noG8wUfiNagIdDdvKke rfj2cJeUjjLQzqTr1rzSvR26xwlJ+Lo1sIbrq9vrjXgJe/O2/dWT9tD+zy/YizOlT6Q7 y8AvtOXyJJyczYaAt+Hk5J7Oqhe2nHEFjUyWAXSTocGoGZCX5Sn1L2GTXx4W8MzYj16z H9jjzGwayvlZmXV6qrqv0EgVqVi8iacMxVH7XCeZAw/ZlTfwEvvv77h/VlQpYf06Oc4c Kfbg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=FYNVHlKgDQ46X+XbR/60sAiRfHp1T0eWqZr2l7PitAY=; b=FZSxnQDF9HqL6VutBPP83+EG7q1VD9rm3rpkZ5KgQ+vADJ85hp/oWfW2H6d2ONkJkc xS0nkcvNFOztmFbMoKHDSFQaU7c+BLCNgAVFHhKUWlQHRowWooWSgmXyKHS1K1u+Pe+0 rQ5ErFZnLmCCzWBbxgkDfCi5mMlno0GtzQAIfsg8Ce7L0NSQde5fFOuzkObbjS1yP4DY SR8DugdK6tNeRBYN84PSmNw9Bk4hGgxYCBA2/xYGX37acqfOlakZ8eeeIc4xeF7C4y+L ZGrl/pGvvpX7tBzdyN2GDkNCJlfVVaKwoRM4p1TgMiL9LDOoWzOtBu1QOWQYiaNGPlZu Wt3g== X-Gm-Message-State: APjAAAXsEzZ2XkeyWbEWbvhotlC8u7eF9kIFUs4847ysFrHUtn9usBmI AC/cZxnMuK+JlHIZ01Y56DQ= X-Google-Smtp-Source: APXvYqzD9cWPQf5UM0f9Pf6Mkn/wkKPaIxfck7hrx6xRV/WzgwEsGJg0M8N/ODEy4+fT++tQp0ZHYQ== X-Received: by 2002:a37:e317:: with SMTP id y23mr28832696qki.431.1582217554540; Thu, 20 Feb 2020 08:52:34 -0800 (PST) Received: from dschatzberg-fedora-PC0Y6AEN.thefacebook.com ([2620:10d:c091:500::3:edb0]) by smtp.gmail.com with ESMTPSA id t55sm43567qte.24.2020.02.20.08.52.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 20 Feb 2020 08:52:33 -0800 (PST) From: Dan Schatzberg 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: Thu, 20 Feb 2020 11:51:51 -0500 Message-Id: <118a1bd99d12f1980c7fc01ab732b40ffd8f0537.1582216294.git.schatzberg.dan@gmail.com> X-Mailer: git-send-email 2.21.1 In-Reply-To: References: MIME-Version: 1.0 To: unlisted-recipients:; (no To-header on input) Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org 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 | 188 +++++++++++++++++++++++++++++++++++++------ drivers/block/loop.h | 11 ++- 2 files changed, 170 insertions(+), 29 deletions(-) diff --git a/drivers/block/loop.c b/drivers/block/loop.c index 739b372a5112..78e5005c6742 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); @@ -891,27 +892,101 @@ static void loop_config_discard(struct loop_device *lo) 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 |= PF_LESS_THROTTLE | PF_MEMALLOC_NOIO; - return kthread_worker_fn(worker_ptr); + destroy_workqueue(lo->workqueue); } static int loop_prepare_queue(struct loop_device *lo) { - 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)) + lo->workqueue = 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; } +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 = &(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_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 ((long)cur_worker->css == (long)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_lock); +} + static void loop_update_rotational(struct loop_device *lo) { struct file *file = lo->lo_backing_file; @@ -993,6 +1068,12 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode, 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; @@ -1155,6 +1236,7 @@ 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); + del_timer_sync(&lo->timer); out_unlock: mutex_unlock(&loop_ctl_mutex); if (partscan) { @@ -1932,7 +2014,7 @@ 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; } @@ -1958,26 +2040,82 @@ 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) { - struct loop_cmd *cmd = - container_of(work, struct loop_cmd, work); + 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; + while (1) { + spin_lock_irq(&lo->lo_lock); + if (list_empty(cmd_list)) + break; + + cmd = 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(); + } - loop_handle_cmd(cmd); + /* + * 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_lock); + current->flags = orig_flags; } -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 = blk_mq_rq_to_pdu(rq); + struct loop_worker *worker = + container_of(work, struct loop_worker, work); + loop_process_work(worker, &worker->cmd_list, worker->lo); +} - kthread_init_work(&cmd->work, loop_queue_work); - return 0; +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 void loop_free_idle_workers(struct timer_list *timer) +{ + struct loop_device *lo = container_of(timer, struct loop_device, timer); + 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); } static const struct blk_mq_ops loop_mq_ops = { .queue_rq = loop_queue_rq, - .init_request = loop_init_request, .complete = lo_complete_rq, }; 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 /* Possible states of device */ @@ -54,8 +53,12 @@ struct loop_device { 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; @@ -65,7 +68,7 @@ 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;