From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (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 C63B019F40A for ; Thu, 2 Apr 2026 00:22:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775089370; cv=none; b=W3aiScM0cNk3J3qmqPmRuOxXinwBQkA+dKLZNmZ3dzFGGC1x/LRRVFN0KcP9hqfNmY9K9ZZnKDMiGmfaskIUdNXg5RhNLlHNOxxNXbZvRRkoab9ikPJ3gVcJmQufgkSlS6GSVXxd2Pn8eIRGajv+ms1kTlXiz4Bqii+yjKaG6JM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775089370; c=relaxed/simple; bh=5CRMHl/Rqo4IGHxD+2SJpsRDBrLyJuBEgy1KMxK/buU=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ZBzt7ALFph2zoqFpFzwGNsgCmrpaAfeSOwg2S7N3Uu+8bV6nPpS5JimstU4tAI+4wUKqW/7AokD3/NJ/5XF2hv57+kMZa6LtiKes8jp4lZztwjq8Z7qn+6WxXYnR3OxyLmZF8LHeXWf4xZlZ0hrg1dhQbLjGaEDxSPKMN6MqxT4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=Js4OBXXL; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Js4OBXXL" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1775089366; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=NlkIZN1Pdr6pNDUfmFvV3yq+JtJ/V9pLJnouaitb3YA=; b=Js4OBXXL7+4QToQSvfGUlA9u9E55vm1zkMHYsluvmIvIrlKpGAVBp5xaH5GH7y3oKuDEGz /F3qcdCMLUli0xA8W3r7S4YRs64BG50Ys/18gcaZVxFrDtthhdv9q4dxRcT5M26yYB5rzh ASc04mfywqhB88qE1WUnv3Va+lsazfk= Received: from mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-670-Rcc8fe1WNMCasc1wit2v8Q-1; Wed, 01 Apr 2026 20:22:43 -0400 X-MC-Unique: Rcc8fe1WNMCasc1wit2v8Q-1 X-Mimecast-MFC-AGG-ID: Rcc8fe1WNMCasc1wit2v8Q_1775089362 Received: from mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.93]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 20E7018005B0; Thu, 2 Apr 2026 00:22:42 +0000 (UTC) Received: from localhost (unknown [10.72.112.46]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id EF2F01800767; Thu, 2 Apr 2026 00:22:40 +0000 (UTC) Date: Thu, 2 Apr 2026 08:22:36 +0800 From: Baoquan He To: "Uladzislau Rezki (Sony)" Cc: linux-mm@kvack.org, Andrew Morton , LKML , stable@vger.kernel.org, lirongqing Subject: Re: [PATCH v3] mm/vmalloc: Use dedicated unbound workqueues for vmap drain Message-ID: References: <20260331202352.879718-1-urezki@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 On 04/01/26 at 05:47pm, Baoquan He wrote: > On 03/31/26 at 10:23pm, Uladzislau Rezki (Sony) wrote: > > 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. > ...snip... > > @@ -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); > > The new schedule_drain_vmap_work() could submit all purge_work on one > CPU, do we need use queue_work_on(cpu, wq, work) instead? Forgot the specified WQ_UNBOUND on alloc_workqueue(), sorry for the noise. Then this patch looks great to me. > > > > > - 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; > > } > ...snip... > > + > > +static int __init vmalloc_init_workqueue(void) > > +{ > > + struct workqueue_struct *drain_wq, *helpers_wq; > > Maybe there's one local variable is enough like below: > > struct workqueue_struct *wq; > unsigned int flags = WQ_UNBOUND | WQ_MEM_RECLAIM; > > wq = alloc_workqueue("vmap_drain", flags, 0); > WARN_ON_ONCE(wq == NULL); > WRITE_ONCE(drain_vmap_wq, wq); > > wq = alloc_workqueue("vmap_drain_helpers", flags, 0); > WARN_ON_ONCE(wq == NULL); > WRITE_ONCE(drain_vmap_helpers_wq, wq); > > return 0; > } > > Just personal preference on nitpick, not strong opionion. >