From mboxrd@z Thu Jan 1 00:00:00 1970 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 751C5C433F5 for ; Thu, 28 Apr 2022 18:00:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1350691AbiD1SEA (ORCPT ); Thu, 28 Apr 2022 14:04:00 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60642 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S245205AbiD1SDv (ORCPT ); Thu, 28 Apr 2022 14:03:51 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 9B95F6D4E6 for ; Thu, 28 Apr 2022 11:00:35 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1651168834; 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=ucwNfXo7EC2ylMgnQC7a+XOsq8PpBGOXOmGWl4N0p00=; b=Ub8y+cF/Ob2mvSHWzJ+NB6xna0mKAsE7KPdxh6Tcl7Qaw1PKDt7joAFakF1qScUlW4wE/O b2Tohq4Ly6/rycJkRDpGCgH7xLPzkNyxJgwEJP8EqNE54Cmz69qbf90OuvkT84pX9iXjWt Bg3aBj4UJdEs6dzsoJgcjrzUr1smmTc= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-580-qnTGZa2qOT6-Ig4cwWNmKQ-1; Thu, 28 Apr 2022 14:00:31 -0400 X-MC-Unique: qnTGZa2qOT6-Ig4cwWNmKQ-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 5C0AC1014A63; Thu, 28 Apr 2022 18:00:30 +0000 (UTC) Received: from fuller.cnet (ovpn-112-2.gru2.redhat.com [10.97.112.2]) by smtp.corp.redhat.com (Postfix) with ESMTPS id AEA08401474; Thu, 28 Apr 2022 18:00:29 +0000 (UTC) Received: by fuller.cnet (Postfix, from userid 1000) id D51B7416F5C3; Thu, 28 Apr 2022 15:00:11 -0300 (-03) Date: Thu, 28 Apr 2022 15:00:11 -0300 From: Marcelo Tosatti To: Borislav Petkov , michael@michaellarabel.com Cc: Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Minchan Kim , Matthew Wilcox , Mel Gorman , Nicolas Saenz Julienne , Juri Lelli , Thomas Gleixner , Sebastian Andrzej Siewior , "Paul E. McKenney" Subject: Re: [patch v5] mm: lru_cache_disable: replace work queue synchronization with synchronize_rcu Message-ID: References: <20220304163554.8872fe5d5a9d634f7a2884f5@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 2.85 on 10.11.54.10 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Mar 31, 2022 at 03:52:45PM +0200, Borislav Petkov wrote: > On Thu, Mar 10, 2022 at 10:22:12AM -0300, Marcelo Tosatti wrote: > > > > On systems that run FIFO:1 applications that busy loop, > > any SCHED_OTHER task that attempts to execute > > on such a CPU (such as work threads) will not > > be scheduled, which leads to system hangs. > > > > 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. > > > > To fix this, replace the usage of work items with synchronize_rcu, > > which provides the same 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. > > > > Signed-off-by: Marcelo Tosatti > > Reviewed-by: Nicolas Saenz Julienne > > Acked-by: Minchan Kim > > Someone pointed me at this: > > https://www.phoronix.com/scan.php?page=news_item&px=Linux-518-Stress-NUMA-Goes-Boom > > which says this one causes a performance regression with stress-ng's > NUMA test... Michael, This is probably do_migrate_pages that is taking too long due to synchronize_rcu(). Switching to synchronize_rcu_expedited() should probably fix it... Can you give it a try, please? diff --git a/mm/swap.c b/mm/swap.c index bceff0cb559c..04a8bbf9817a 100644 --- a/mm/swap.c +++ b/mm/swap.c @@ -879,7 +879,7 @@ void lru_cache_disable(void) * lru_disable_count = 0 will have exited the critical * section when synchronize_rcu() returns. */ - synchronize_rcu(); + synchronize_rcu_expedited(); #ifdef CONFIG_SMP __lru_add_drain_all(true); #else