From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2C02E2BAF7; Wed, 25 Feb 2026 01:30:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771983038; cv=none; b=lO1Lm0Zcljrv0hqROMzJ9PtDnCBgPYZsH7kp42TXoeo/6ft3xtCEoNd6RZnykHDWoegc9+ZQCD7xCGmTsqPf1P4hJT+AtwDzo+ILdp4E+mpLiQooJMIk2NlfK8+Q8uGCzyTCBTmmKkWUyToT/STvpradheuctfR0ZsTDgV25iOE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771983038; c=relaxed/simple; bh=uMgBkNEq/Hy+sXVN+QOG+1FqW9p6qWje/0ZVFq4eWHo=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=L1F7t1An3Wiglks3iLqADCtmCT+L8uDDVEkdFepAVuKgokP3ABDFP6CWWWa/JpGtY4aNq1Nm9DN5Z+RGp9OZc+lsfDIZ+FzFG5No+Zt7tJ7cB2ZMDNWm0CP4afPcGmzoo4NvMChTb19fZ/tEQQ8vO5/YFupmF0bwCnGyeiDNPK0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=gETTwnqX; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="gETTwnqX" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E35E6C19423; Wed, 25 Feb 2026 01:30:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1771983038; bh=uMgBkNEq/Hy+sXVN+QOG+1FqW9p6qWje/0ZVFq4eWHo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=gETTwnqXQGcxbEzOFERpzz+yFdI3hjXrs9ILPeOyrUnHBBZkqDXncKYsDIkHWmyXs Bt6/SjF4XmfydECdpi5Koiog6R0GOooPsB+2C4ammtdGctlPK0Rx0MmmOXGrHYux9V K6Q7JNXZBBkHZu65lx7OdTNtAL8CyUHH87kfnZMI= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, ying chen , Lai Jiangshan , Tejun Heo , Sasha Levin Subject: [PATCH 6.19 201/781] workqueue: Process rescuer work items one-by-one using a cursor Date: Tue, 24 Feb 2026 17:15:10 -0800 Message-ID: <20260225012404.594350645@linuxfoundation.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260225012359.695468795@linuxfoundation.org> References: <20260225012359.695468795@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.19-stable review patch. If anyone has any objections, please let me know. ------------------ From: Lai Jiangshan [ Upstream commit e5a30c303b07a4d6083e0f7f051b53add6d93c5d ] Previously, the rescuer scanned for all matching work items at once and processed them within a single rescuer thread, which could cause one blocking work item to stall all others. Make the rescuer process work items one-by-one instead of slurping all matches in a single pass. Break the rescuer loop after finding and processing the first matching work item, then restart the search to pick up the next. This gives normal worker threads a chance to process other items which gives them the opportunity to be processed instead of waiting on the rescuer's queue and prevents a blocking work item from stalling the rest once memory pressure is relieved. Introduce a dummy cursor work item to avoid potentially O(N^2) rescans of the work list. The marker records the resume position for the next scan, eliminating redundant traversals. Also introduce RESCUER_BATCH to control the maximum number of work items the rescuer processes in each turn, and move on to other PWQs when the limit is reached. Cc: ying chen Reported-by: ying chen Fixes: e22bee782b3b ("workqueue: implement concurrency managed dynamic worker pool") Signed-off-by: Lai Jiangshan Signed-off-by: Tejun Heo Signed-off-by: Sasha Levin --- kernel/workqueue.c | 75 ++++++++++++++++++++++++++++++++++++---------- 1 file changed, 59 insertions(+), 16 deletions(-) diff --git a/kernel/workqueue.c b/kernel/workqueue.c index 253311af47c6d..2909c19540ed1 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -117,6 +117,8 @@ enum wq_internal_consts { MAYDAY_INTERVAL = HZ / 10, /* and then every 100ms */ CREATE_COOLDOWN = HZ, /* time to breath after fail */ + RESCUER_BATCH = 16, /* process items per turn */ + /* * Rescue workers are used only on emergencies and shared by * all cpus. Give MIN_NICE. @@ -286,6 +288,7 @@ struct pool_workqueue { struct list_head pending_node; /* LN: node on wq_node_nr_active->pending_pwqs */ struct list_head pwqs_node; /* WR: node on wq->pwqs */ struct list_head mayday_node; /* MD: node on wq->maydays */ + struct work_struct mayday_cursor; /* L: cursor on pool->worklist */ u64 stats[PWQ_NR_STATS]; @@ -1120,6 +1123,12 @@ static struct worker *find_worker_executing_work(struct worker_pool *pool, return NULL; } +static void mayday_cursor_func(struct work_struct *work) +{ + /* should not be processed, only for marking position */ + BUG(); +} + /** * move_linked_works - move linked works to a list * @work: start of series of works to be scheduled @@ -1182,6 +1191,16 @@ static bool assign_work(struct work_struct *work, struct worker *worker, lockdep_assert_held(&pool->lock); + /* The cursor work should not be processed */ + if (unlikely(work->func == mayday_cursor_func)) { + /* only worker_thread() can possibly take this branch */ + WARN_ON_ONCE(worker->rescue_wq); + if (nextp) + *nextp = list_next_entry(work, entry); + list_del_init(&work->entry); + return false; + } + /* * A single work shouldn't be executed concurrently by multiple workers. * __queue_work() ensures that @work doesn't jump to a different pool @@ -3440,22 +3459,30 @@ static int worker_thread(void *__worker) static bool assign_rescuer_work(struct pool_workqueue *pwq, struct worker *rescuer) { struct worker_pool *pool = pwq->pool; + struct work_struct *cursor = &pwq->mayday_cursor; struct work_struct *work, *n; /* need rescue? */ if (!pwq->nr_active || !need_to_create_worker(pool)) return false; - /* - * Slurp in all works issued via this workqueue and - * process'em. - */ - list_for_each_entry_safe(work, n, &pool->worklist, entry) { - if (get_work_pwq(work) == pwq && assign_work(work, rescuer, &n)) + /* search from the start or cursor if available */ + if (list_empty(&cursor->entry)) + work = list_first_entry(&pool->worklist, struct work_struct, entry); + else + work = list_next_entry(cursor, entry); + + /* find the next work item to rescue */ + list_for_each_entry_safe_from(work, n, &pool->worklist, entry) { + if (get_work_pwq(work) == pwq && assign_work(work, rescuer, &n)) { pwq->stats[PWQ_STAT_RESCUED]++; + /* put the cursor for next search */ + list_move_tail(&cursor->entry, &n->entry); + return true; + } } - return !list_empty(&rescuer->scheduled); + return false; } /** @@ -3512,6 +3539,7 @@ static int rescuer_thread(void *__rescuer) struct pool_workqueue *pwq = list_first_entry(&wq->maydays, struct pool_workqueue, mayday_node); struct worker_pool *pool = pwq->pool; + unsigned int count = 0; __set_current_state(TASK_RUNNING); list_del_init(&pwq->mayday_node); @@ -3524,19 +3552,16 @@ static int rescuer_thread(void *__rescuer) WARN_ON_ONCE(!list_empty(&rescuer->scheduled)); - if (assign_rescuer_work(pwq, rescuer)) { + while (assign_rescuer_work(pwq, rescuer)) { process_scheduled_works(rescuer); /* - * The above execution of rescued work items could - * have created more to rescue through - * pwq_activate_first_inactive() or chained - * queueing. Let's put @pwq back on mayday list so - * that such back-to-back work items, which may be - * being used to relieve memory pressure, don't - * incur MAYDAY_INTERVAL delay inbetween. + * If the per-turn work item limit is reached and other + * PWQs are in mayday, requeue mayday for this PWQ and + * let the rescuer handle the other PWQs first. */ - if (pwq->nr_active && need_to_create_worker(pool)) { + if (++count > RESCUER_BATCH && !list_empty(&pwq->wq->maydays) && + pwq->nr_active && need_to_create_worker(pool)) { raw_spin_lock(&wq_mayday_lock); /* * Queue iff somebody else hasn't queued it already. @@ -3546,9 +3571,14 @@ static int rescuer_thread(void *__rescuer) list_add_tail(&pwq->mayday_node, &wq->maydays); } raw_spin_unlock(&wq_mayday_lock); + break; } } + /* The cursor can not be left behind without the rescuer watching it. */ + if (!list_empty(&pwq->mayday_cursor.entry) && list_empty(&pwq->mayday_node)) + list_del_init(&pwq->mayday_cursor.entry); + /* * Leave this pool. Notify regular workers; otherwise, we end up * with 0 concurrency and stalling the execution. @@ -5167,6 +5197,19 @@ static void init_pwq(struct pool_workqueue *pwq, struct workqueue_struct *wq, INIT_LIST_HEAD(&pwq->pwqs_node); INIT_LIST_HEAD(&pwq->mayday_node); kthread_init_work(&pwq->release_work, pwq_release_workfn); + + /* + * Set the dummy cursor work with valid function and get_work_pwq(). + * + * The cursor work should only be in the pwq->pool->worklist, and + * should not be treated as a processable work item. + * + * WORK_STRUCT_PENDING and WORK_STRUCT_INACTIVE just make it less + * surprise for kernel debugging tools and reviewers. + */ + INIT_WORK(&pwq->mayday_cursor, mayday_cursor_func); + atomic_long_set(&pwq->mayday_cursor.data, (unsigned long)pwq | + WORK_STRUCT_PENDING | WORK_STRUCT_PWQ | WORK_STRUCT_INACTIVE); } /* sync @pwq with the current state of its associated wq and link it */ -- 2.51.0