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Mon, 30 Mar 2026 09:05:53 -0700 (PDT) Received: from localhost.localdomain ([2001:9b1:d5a0:a500::24b]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-5a2b1456eb9sm1733066e87.69.2026.03.30.09.05.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 30 Mar 2026 09:05:53 -0700 (PDT) From: "Uladzislau Rezki (Sony)" To: linux-mm@kvack.org, Andrew Morton Cc: Baoquan He , LKML , Uladzislau Rezki , lirongqing Subject: [PATCH] mm/vmalloc: Use dedicated unbound workqueue for vmap purge/drain Date: Mon, 30 Mar 2026 18:05:52 +0200 Message-ID: <20260330160552.485430-1-urezki@gmail.com> X-Mailer: git-send-email 2.47.3 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" The drain_vmap_area_work() function can take >10ms to complete when there are many accumulated vmap areas in a system with a high CPU count, causing workqueue watchdog warnings when run via schedule_work(): [ 2069.796205] workqueue: drain_vmap_area_work hogged CPU for >10000us 4 ti= mes, consider switching to WQ_UNBOUND [ 2192.823225] workqueue: drain_vmap_area_work hogged CPU for >10000us 5 ti= mes, consider switching to WQ_UNBOUND Switch to a dedicated WQ_UNBOUND workqueue to allow the scheduler to run this background task on any available CPU, improving responsiveness. Use WQ_MEM_RECLAIM to ensure forward progress under memory pressure. Also simplify purge helper scheduling by removing cpumask-based iteration in favour to iterating directly over vmap nodes with pending work. Cc: lirongqing Link: https://lore.kernel.org/all/20260319074307.2325-1-lirongqing@baidu.co= m/ Signed-off-by: Uladzislau Rezki (Sony) --- mm/vmalloc.c | 63 ++++++++++++++++++++++++++++++++-------------------- 1 file changed, 39 insertions(+), 24 deletions(-) diff --git a/mm/vmalloc.c b/mm/vmalloc.c index 61caa55a4402..7c1ab4a57409 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; =20 /* @@ -1067,6 +1068,7 @@ 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_wq; =20 static __cacheline_aligned_in_smp atomic_long_t nr_vmalloc_pages; static __cacheline_aligned_in_smp atomic_long_t vmap_lazy_nr; @@ -2335,6 +2337,19 @@ static void purge_vmap_node(struct work_struct *work) reclaim_list_global(&local_list); } =20 +static bool +schedule_drain_vmap_work(struct work_struct *work) +{ + struct workqueue_struct *wq =3D READ_ONCE(drain_vmap_wq); + + if (wq) { + queue_work(wq, work); + return true; + } + + return false; +} + /* * Purges all lazily-freed vmap areas. */ @@ -2342,19 +2357,12 @@ static bool __purge_vmap_area_lazy(unsigned long st= art, unsigned long end, bool full_pool_decay) { unsigned long nr_purged_areas =3D 0; + unsigned int nr_purge_nodes =3D 0; unsigned int nr_purge_helpers; - static cpumask_t purge_nodes; - unsigned int nr_purge_nodes; struct vmap_node *vn; - int i; =20 lockdep_assert_held(&vmap_purge_lock); =20 - /* - * Use cpumask to mark which node has to be processed. - */ - purge_nodes =3D CPU_MASK_NONE; - for_each_vmap_node(vn) { INIT_LIST_HEAD(&vn->purge_list); vn->skip_populate =3D full_pool_decay; @@ -2374,10 +2382,9 @@ static bool __purge_vmap_area_lazy(unsigned long sta= rt, unsigned long end, end =3D max(end, list_last_entry(&vn->purge_list, struct vmap_area, list)->va_end); =20 - cpumask_set_cpu(node_to_id(vn), &purge_nodes); + nr_purge_nodes++; } =20 - nr_purge_nodes =3D cpumask_weight(&purge_nodes); if (nr_purge_nodes > 0) { flush_tlb_kernel_range(start, end); =20 @@ -2385,29 +2392,25 @@ static bool __purge_vmap_area_lazy(unsigned long st= art, unsigned long end, nr_purge_helpers =3D atomic_long_read(&vmap_lazy_nr) / lazy_max_pages(); nr_purge_helpers =3D clamp(nr_purge_helpers, 1U, nr_purge_nodes) - 1; =20 - for_each_cpu(i, &purge_nodes) { - vn =3D &vmap_nodes[i]; + for_each_vmap_node(vn) { + vn->work_queued =3D false; + + if (list_empty(&vn->purge_list)) + continue; =20 if (nr_purge_helpers > 0) { INIT_WORK(&vn->purge_work, purge_vmap_node); - - if (cpumask_test_cpu(i, cpu_online_mask)) - schedule_work_on(i, &vn->purge_work); - else - schedule_work(&vn->purge_work); - + vn->work_queued =3D schedule_drain_vmap_work(&vn->purge_work); nr_purge_helpers--; } else { - vn->purge_work.func =3D NULL; purge_vmap_node(&vn->purge_work); nr_purged_areas +=3D vn->nr_purged; } } =20 - for_each_cpu(i, &purge_nodes) { - vn =3D &vmap_nodes[i]; - - 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 +=3D vn->nr_purged; } @@ -2471,7 +2474,7 @@ static void free_vmap_area_noflush(struct vmap_area *= va) =20 /* 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(&drain_vmap_work); } =20 /* @@ -5483,3 +5486,15 @@ void __init vmalloc_init(void) vmap_node_shrinker->scan_objects =3D vmap_node_shrink_scan; shrinker_register(vmap_node_shrinker); } + +static int __init vmalloc_init_workqueue(void) +{ + struct workqueue_struct *wq; + + wq =3D alloc_workqueue("vmap_drain", WQ_UNBOUND | WQ_MEM_RECLAIM, 0); + WARN_ON(wq =3D=3D NULL); + WRITE_ONCE(drain_vmap_wq, wq); + + return 0; +} +early_initcall(vmalloc_init_workqueue); --=20 2.47.3