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 CFD68C433F5 for ; Thu, 31 Mar 2022 13:52:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237057AbiCaNyl (ORCPT ); Thu, 31 Mar 2022 09:54:41 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60586 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231445AbiCaNyj (ORCPT ); Thu, 31 Mar 2022 09:54:39 -0400 Received: from mail.skyhub.de (mail.skyhub.de [5.9.137.197]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 53D6E216A70 for ; Thu, 31 Mar 2022 06:52:51 -0700 (PDT) Received: from zn.tnic (p2e55dff8.dip0.t-ipconnect.de [46.85.223.248]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.skyhub.de (SuperMail on ZX Spectrum 128k) with ESMTPSA id 877151EC0535; Thu, 31 Mar 2022 15:52:46 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1648734766; 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: content-transfer-encoding:in-reply-to:in-reply-to: references:references; bh=f0b47ts2VheeKS+3ncRDbOuaDfRJ+I8108gtQgFa0aM=; b=LTUp+g4rs1ac0r9x/TD4H6FmSRcqezk1vUXbkASKLxk9n3Dwb+JcE1jOW3oFj1bpEhuFei AtQJ1OhZuF94JpMgzup2A8m+nbK69gAkatr0QlQ1lsvNgVIshFIEbnfwcdMrn+1f1fIJN8 n+Zf3KtyAVMI5GBQR+Q59kTk5VBX0KI= Date: Thu, 31 Mar 2022 15:52:45 +0200 From: Borislav Petkov To: Marcelo Tosatti 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=utf-8 Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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... -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette