From patchwork Fri Mar 4 16:29:31 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Marcelo Tosatti X-Patchwork-Id: 12769445 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 988C7C433EF for ; Fri, 4 Mar 2022 16:30:06 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 2F5A08D0003; Fri, 4 Mar 2022 11:30:06 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 27DBE8D0001; Fri, 4 Mar 2022 11:30:06 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 11EE88D0003; Fri, 4 Mar 2022 11:30:06 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0134.hostedemail.com [216.40.44.134]) by kanga.kvack.org (Postfix) with ESMTP id 005328D0001 for ; Fri, 4 Mar 2022 11:30:05 -0500 (EST) Received: from smtpin31.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 9DB458249980 for ; Fri, 4 Mar 2022 16:30:05 +0000 (UTC) X-FDA: 79207240770.31.7BE3866 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by imf13.hostedemail.com (Postfix) with ESMTP id DF22120028 for ; Fri, 4 Mar 2022 16:30:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1646411404; 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=Xv2/sRhNziwPgVlcororfSR3ylmU1ZdZfltQ24OShvQ=; b=KtgxxwEXOnJp0Tad/M8uP6HajeY/z5zxTv1dAQ3txackKEz7POlU4ivbVgw4tnp0Oyx6PM QoFWWg5febB6D5nXHYepwJABWv4IyC6mAkfjzcGMcy792Lk27hpDmDKK79Wt4Sl7I/N3VD 5L7ivl7Zlhi8yiWi1rtlI+h0VCXqd1g= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-282-8ABN0QEoP-2-6DOk8DD8bQ-1; Fri, 04 Mar 2022 11:30:03 -0500 X-MC-Unique: 8ABN0QEoP-2-6DOk8DD8bQ-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 93A7F1006AA6; Fri, 4 Mar 2022 16:30:01 +0000 (UTC) Received: from fuller.cnet (ovpn-112-4.gru2.redhat.com [10.97.112.4]) by smtp.corp.redhat.com (Postfix) with ESMTPS id D206686B92; Fri, 4 Mar 2022 16:29:51 +0000 (UTC) Received: by fuller.cnet (Postfix, from userid 1000) id EAFAF416D862; Fri, 4 Mar 2022 13:29:31 -0300 (-03) Date: Fri, 4 Mar 2022 13:29:31 -0300 From: Marcelo Tosatti To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, Minchan Kim , Matthew Wilcox , Mel Gorman , Nicolas Saenz Julienne , Juri Lelli , Thomas Gleixner , Sebastian Andrzej Siewior , "Paul E. McKenney" , Andrew Morton Subject: [patch v4] mm: lru_cache_disable: replace work queue synchronization with synchronize_rcu Message-ID: References: MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: DF22120028 X-Stat-Signature: 9snea9kp7h9r9dotwmaep1admpngey9h Authentication-Results: imf13.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=KtgxxwEX; spf=none (imf13.hostedemail.com: domain of mtosatti@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=mtosatti@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-Rspam-User: X-HE-Tag: 1646411404-551530 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On systems that run FIFO:1 applications that busy loop on isolated CPUs, executing tasks on such CPUs under lower priority is undesired (since that will either hang the system, or cause longer interruption to the FIFO task due to execution of lower priority task with very small sched slices). Commit d479960e44f27e0e52ba31b21740b703c538027c ("mm: disable LRU pagevec during the migration temporarily") relies on queueing work items on all online CPUs to ensure visibility of lru_disable_count. However, its possible to use synchronize_rcu which will provide the same guarantees (see comment this patch modifies on lru_cache_disable). Fixes: [ 1873.243925] INFO: task kworker/u160:0:9 blocked for more than 622 seconds. [ 1873.243927] Tainted: G I --------- --- 5.14.0-31.rt21.31.el9.x86_64 #1 [ 1873.243929] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [ 1873.243929] task:kworker/u160:0 state:D stack: 0 pid: 9 ppid: 2 flags:0x00004000 [ 1873.243932] Workqueue: cpuset_migrate_mm cpuset_migrate_mm_workfn [ 1873.243936] Call Trace: [ 1873.243938] __schedule+0x21b/0x5b0 [ 1873.243941] schedule+0x43/0xe0 [ 1873.243943] schedule_timeout+0x14d/0x190 [ 1873.243946] ? resched_curr+0x20/0xe0 [ 1873.243953] ? __prepare_to_swait+0x4b/0x70 [ 1873.243958] wait_for_completion+0x84/0xe0 [ 1873.243962] __flush_work.isra.0+0x146/0x200 [ 1873.243966] ? flush_workqueue_prep_pwqs+0x130/0x130 [ 1873.243971] __lru_add_drain_all+0x158/0x1f0 [ 1873.243978] do_migrate_pages+0x3d/0x2d0 [ 1873.243985] ? pick_next_task_fair+0x39/0x3b0 [ 1873.243989] ? put_prev_task_fair+0x1e/0x30 [ 1873.243992] ? pick_next_task+0xb30/0xbd0 [ 1873.243995] ? __tick_nohz_task_switch+0x1e/0x70 [ 1873.244000] ? raw_spin_rq_unlock+0x18/0x60 [ 1873.244002] ? finish_task_switch.isra.0+0xc1/0x2d0 [ 1873.244005] ? __switch_to+0x12f/0x510 [ 1873.244013] cpuset_migrate_mm_workfn+0x22/0x40 [ 1873.244016] process_one_work+0x1e0/0x410 [ 1873.244019] worker_thread+0x50/0x3b0 [ 1873.244022] ? process_one_work+0x410/0x410 [ 1873.244024] kthread+0x173/0x190 [ 1873.244027] ? set_kthread_struct+0x40/0x40 [ 1873.244031] ret_from_fork+0x1f/0x30 Signed-off-by: Marcelo Tosatti --- v4: improve comment clarify, mention synchronize_rcu guarantees on v5.1 (Andrew Morton / Paul E. McKenney) v3: update stale comment (Nicolas Saenz Julienne) v2: rt_spin_lock calls rcu_read_lock, no need to add it before local_lock on swap.c (Nicolas Saenz Julienne) Acked-by: Minchan Kim diff --git a/mm/swap.c b/mm/swap.c index bcf3ac288b56..b5ee163daa66 100644 --- a/mm/swap.c +++ b/mm/swap.c @@ -831,8 +831,7 @@ inline void __lru_add_drain_all(bool force_all_cpus) for_each_online_cpu(cpu) { struct work_struct *work = &per_cpu(lru_add_drain_work, cpu); - if (force_all_cpus || - pagevec_count(&per_cpu(lru_pvecs.lru_add, cpu)) || + if (pagevec_count(&per_cpu(lru_pvecs.lru_add, cpu)) || data_race(pagevec_count(&per_cpu(lru_rotate.pvec, cpu))) || pagevec_count(&per_cpu(lru_pvecs.lru_deactivate_file, cpu)) || pagevec_count(&per_cpu(lru_pvecs.lru_deactivate, cpu)) || @@ -876,15 +875,21 @@ atomic_t lru_disable_count = ATOMIC_INIT(0); void lru_cache_disable(void) { atomic_inc(&lru_disable_count); -#ifdef CONFIG_SMP /* - * lru_add_drain_all in the force mode will schedule draining on - * all online CPUs so any calls of lru_cache_disabled wrapped by - * local_lock or preemption disabled would be ordered by that. - * The atomic operation doesn't need to have stronger ordering - * requirements because that is enforced by the scheduling - * guarantees. + * Readers of lru_disable_count are protected by either disabling + * preemption or rcu_read_lock: + * + * preempt_disable, local_irq_disable [bh_lru_lock()] + * rcu_read_lock [rt_spin_lock CONFIG_PREEMPT_RT] + * preempt_disable [local_lock !CONFIG_PREEMPT_RT] + * + * Since v5.1 kernel, synchronize_rcu() is guaranteed to wait on + * preempt_disable() regions of code. So any CPU which sees + * lru_disable_count = 0 will have exited the critical + * section when synchronize_rcu() returns. */ + synchronize_rcu(); +#ifdef CONFIG_SMP __lru_add_drain_all(true); #else lru_add_and_bh_lrus_drain();