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Tue, 31 Mar 2026 13:23:54 -0700 (PDT) Received: from localhost.localdomain ([2001:9b1:d5a0:a500::24b]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-5a2b13f4329sm2681171e87.3.2026.03.31.13.23.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 31 Mar 2026 13:23:54 -0700 (PDT) From: "Uladzislau Rezki (Sony)" To: linux-mm@kvack.org, Andrew Morton Cc: Baoquan He , LKML , Uladzislau Rezki , stable@vger.kernel.org, lirongqing Subject: [PATCH v3] mm/vmalloc: Use dedicated unbound workqueues for vmap drain Date: Tue, 31 Mar 2026 22:23:52 +0200 Message-ID: <20260331202352.879718-1-urezki@gmail.com> X-Mailer: git-send-email 2.47.3 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: B61A740003 X-Stat-Signature: ht6fzxusuwpxgzpby1d1q3amhomi3on1 X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1774988636-746686 X-HE-Meta: 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 3tWDvync 1QxoZNXl7BFF7KYAFAJEqhBbOEEqQTdn28hM9T2ggX24MVIR4PKsnonQue2Jo6ty00Yv/vv0eu1lxzcczlVEihIIIedwtarkkXrtFwbihmqZy73VFG1yN7CaJ2mW3Hagug4bpApEQ0rIir2Cbyh7oUe/foid/dUxHKlq8EotHnH5ofzoo4erl3dvb6GbFWfmJimiDq+Uqk3XInEPmejFIYQL5OX8OU0vNcr7ex8aio12G2jeI00kq5G4IceLu+Cw34oVjtXDiOZq/5ZmLZJYOLRP9gX9w9dqcVS7jpdGqZgyLtcJ59rbDNEnCrJ6GN7bBQsv5X/+SAjWdNjjFncsZnkJvWiw71U0XbKtvvlyELw/ndZm/EhWeBygIggJYidM/6ARRKRq3WtYBLxCgKhKH1YRKLVWpRPqHOtCnNdn5aCSwZYU= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: drain_vmap_area_work() function can take >10ms to complete when there are many accumulated vmap areas in a system with high CPU count, causing workqueue watchdog warnings when run via schedule_work(): workqueue: drain_vmap_area_work hogged CPU for >10000us Move the top-level drain work to a dedicated WQ_UNBOUND workqueue so the scheduler can run this background work on any available CPU, improving responsiveness. Use the WQ_MEM_RECLAIM to ensure forward progress under memory pressure. Move purge helpers to separate WQ_UNBOUND | WQ_MEM_RECLAIM workqueue. This allows drain_vmap_work to wait for helpers completion without creating dependency on the same rescuer thread and avoid a potential parent/child deadlock. Simplify purge helper scheduling by removing cpumask-based iteration to iterating directly over vmap nodes checking work_queued state. Cc: stable@vger.kernel.org Cc: lirongqing Fixes: 72210662c5a2 ("mm: vmalloc: offload free_vmap_area_lock lock") Link: https://lore.kernel.org/all/20260319074307.2325-1-lirongqing@baidu.com/ Signed-off-by: Uladzislau Rezki (Sony) --- mm/vmalloc.c | 79 ++++++++++++++++++++++++++++++++++------------------ 1 file changed, 52 insertions(+), 27 deletions(-) diff --git a/mm/vmalloc.c b/mm/vmalloc.c index 61caa55a4402..0fa1208a910b 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -949,6 +949,7 @@ static struct vmap_node { struct list_head purge_list; struct work_struct purge_work; unsigned long nr_purged; + bool work_queued; } single; /* @@ -1067,6 +1068,8 @@ static void reclaim_and_purge_vmap_areas(void); static BLOCKING_NOTIFIER_HEAD(vmap_notify_list); static void drain_vmap_area_work(struct work_struct *work); static DECLARE_WORK(drain_vmap_work, drain_vmap_area_work); +static struct workqueue_struct *drain_vmap_helpers_wq; +static struct workqueue_struct *drain_vmap_wq; static __cacheline_aligned_in_smp atomic_long_t nr_vmalloc_pages; static __cacheline_aligned_in_smp atomic_long_t vmap_lazy_nr; @@ -2335,6 +2338,16 @@ static void purge_vmap_node(struct work_struct *work) reclaim_list_global(&local_list); } +static bool +schedule_drain_vmap_work(struct workqueue_struct *wq, + struct work_struct *work) +{ + if (wq) + return queue_work(wq, work); + + return false; +} + /* * Purges all lazily-freed vmap areas. */ @@ -2342,19 +2355,12 @@ static bool __purge_vmap_area_lazy(unsigned long start, unsigned long end, bool full_pool_decay) { unsigned long nr_purged_areas = 0; + unsigned int nr_purge_nodes = 0; unsigned int nr_purge_helpers; - static cpumask_t purge_nodes; - unsigned int nr_purge_nodes; struct vmap_node *vn; - int i; lockdep_assert_held(&vmap_purge_lock); - /* - * Use cpumask to mark which node has to be processed. - */ - purge_nodes = CPU_MASK_NONE; - for_each_vmap_node(vn) { INIT_LIST_HEAD(&vn->purge_list); vn->skip_populate = full_pool_decay; @@ -2374,10 +2380,9 @@ static bool __purge_vmap_area_lazy(unsigned long start, unsigned long end, end = max(end, list_last_entry(&vn->purge_list, struct vmap_area, list)->va_end); - cpumask_set_cpu(node_to_id(vn), &purge_nodes); + nr_purge_nodes++; } - nr_purge_nodes = cpumask_weight(&purge_nodes); if (nr_purge_nodes > 0) { flush_tlb_kernel_range(start, end); @@ -2385,29 +2390,31 @@ static bool __purge_vmap_area_lazy(unsigned long start, unsigned long end, nr_purge_helpers = atomic_long_read(&vmap_lazy_nr) / lazy_max_pages(); nr_purge_helpers = clamp(nr_purge_helpers, 1U, nr_purge_nodes) - 1; - for_each_cpu(i, &purge_nodes) { - vn = &vmap_nodes[i]; + for_each_vmap_node(vn) { + vn->work_queued = false; + + if (list_empty(&vn->purge_list)) + continue; if (nr_purge_helpers > 0) { INIT_WORK(&vn->purge_work, purge_vmap_node); + vn->work_queued = schedule_drain_vmap_work( + READ_ONCE(drain_vmap_helpers_wq), &vn->purge_work); - if (cpumask_test_cpu(i, cpu_online_mask)) - schedule_work_on(i, &vn->purge_work); - else - schedule_work(&vn->purge_work); - - nr_purge_helpers--; - } else { - vn->purge_work.func = NULL; - purge_vmap_node(&vn->purge_work); - nr_purged_areas += vn->nr_purged; + if (vn->work_queued) { + nr_purge_helpers--; + continue; + } } - } - for_each_cpu(i, &purge_nodes) { - vn = &vmap_nodes[i]; + /* Sync path. Process locally. */ + purge_vmap_node(&vn->purge_work); + nr_purged_areas += vn->nr_purged; + } - if (vn->purge_work.func) { + /* Wait for completion if queued any. */ + for_each_vmap_node(vn) { + if (vn->work_queued) { flush_work(&vn->purge_work); nr_purged_areas += vn->nr_purged; } @@ -2471,7 +2478,8 @@ static void free_vmap_area_noflush(struct vmap_area *va) /* After this point, we may free va at any time */ if (unlikely(nr_lazy > nr_lazy_max)) - schedule_work(&drain_vmap_work); + schedule_drain_vmap_work(READ_ONCE(drain_vmap_wq), + &drain_vmap_work); } /* @@ -5483,3 +5491,20 @@ void __init vmalloc_init(void) vmap_node_shrinker->scan_objects = vmap_node_shrink_scan; shrinker_register(vmap_node_shrinker); } + +static int __init vmalloc_init_workqueue(void) +{ + struct workqueue_struct *drain_wq, *helpers_wq; + unsigned int flags = WQ_UNBOUND | WQ_MEM_RECLAIM; + + drain_wq = alloc_workqueue("vmap_drain", flags, 0); + WARN_ON_ONCE(drain_wq == NULL); + WRITE_ONCE(drain_vmap_wq, drain_wq); + + helpers_wq = alloc_workqueue("vmap_drain_helpers", flags, 0); + WARN_ON_ONCE(helpers_wq == NULL); + WRITE_ONCE(drain_vmap_helpers_wq, helpers_wq); + + return 0; +} +early_initcall(vmalloc_init_workqueue); -- 2.47.3