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 5A5EDC433EF for ; Tue, 17 May 2022 23:36:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231991AbiEQXgP (ORCPT ); Tue, 17 May 2022 19:36:15 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55704 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232142AbiEQXgD (ORCPT ); Tue, 17 May 2022 19:36:03 -0400 Received: from alexa-out.qualcomm.com (alexa-out.qualcomm.com [129.46.98.28]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A74A0BC0B for ; Tue, 17 May 2022 16:35:49 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=quicinc.com; i=@quicinc.com; q=dns/txt; s=qcdkim; t=1652830551; x=1684366551; h=date:from:to:cc:subject:message-id:references: mime-version:in-reply-to; bh=sUOiDeh7EH02CIozxQKBpiv/aZ59cUoQ05kZcZ9BhXc=; b=A/xvRLc4dQFtPrEg5mKY0+drKSYW3SHiy8sn5ojCGkwiYoqshCtxLC/Q 8aRUSHe9X3R6ZOS68+EWY7+7Lubw+KOJZ3YCdAXroUQrGfJ41utv3BJjz 9ySeVAF7UeEKDR58a0drBMhOct5WaSig9Aeyvp1h1uoyZUfp9rwtpAnEu c=; Received: from ironmsg-lv-alpha.qualcomm.com ([10.47.202.13]) by alexa-out.qualcomm.com with ESMTP; 17 May 2022 16:35:49 -0700 X-QCInternal: smtphost Received: from nasanex01c.na.qualcomm.com ([10.47.97.222]) by ironmsg-lv-alpha.qualcomm.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 17 May 2022 16:35:48 -0700 Received: from nalasex01a.na.qualcomm.com (10.47.209.196) by nasanex01c.na.qualcomm.com (10.47.97.222) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.986.22; Tue, 17 May 2022 16:35:08 -0700 Received: from qian (10.80.80.8) by nalasex01a.na.qualcomm.com (10.47.209.196) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.986.22; Tue, 17 May 2022 16:35:07 -0700 Date: Tue, 17 May 2022 19:35:07 -0400 From: Qian Cai To: Mel Gorman CC: Andrew Morton , Nicolas Saenz Julienne , Marcelo Tosatti , Vlastimil Babka , Michal Hocko , LKML , Linux-MM Subject: Re: [PATCH 0/6] Drain remote per-cpu directly v3 Message-ID: <20220517233507.GA423@qian> References: <20220512085043.5234-1-mgorman@techsingularity.net> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20220512085043.5234-1-mgorman@techsingularity.net> X-Originating-IP: [10.80.80.8] X-ClientProxiedBy: nasanex01b.na.qualcomm.com (10.46.141.250) To nalasex01a.na.qualcomm.com (10.47.209.196) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 12, 2022 at 09:50:37AM +0100, Mel Gorman wrote: > Changelog since v2 > o More conversions from page->lru to page->[pcp_list|buddy_list] > o Additional test results in changelogs > > Changelog since v1 > o Fix unsafe RT locking scheme > o Use spin_trylock on UP PREEMPT_RT > > This series has the same intent as Nicolas' series "mm/page_alloc: Remote > per-cpu lists drain support" -- avoid interference of a high priority > task due to a workqueue item draining per-cpu page lists. While many > workloads can tolerate a brief interruption, it may be cause a real-time > task runnning on a NOHZ_FULL CPU to miss a deadline and at minimum, > the draining in non-deterministic. > > Currently an IRQ-safe local_lock protects the page allocator per-cpu lists. > The local_lock on its own prevents migration and the IRQ disabling protects > from corruption due to an interrupt arriving while a page allocation is > in progress. The locking is inherently unsafe for remote access unless > the CPU is hot-removed. > > This series adjusts the locking. A spinlock is added to struct > per_cpu_pages to protect the list contents while local_lock_irq continues > to prevent migration and IRQ reentry. This allows a remote CPU to safely > drain a remote per-cpu list. > > This series is a partial series. Follow-on work should allow the > local_irq_save to be converted to a local_irq to avoid IRQs being > disabled/enabled in most cases. Consequently, there are some TODO comments > highlighting the places that would change if local_irq was used. However, > there are enough corner cases that it deserves a series on its own > separated by one kernel release and the priority right now is to avoid > interference of high priority tasks. Reverting the whole series fixed an issue that offlining a memory section blocking for hours on today's linux-next tree. __wait_rcu_gp synchronize_rcu at kernel/rcu/tree.c:3915 lru_cache_disable at mm/swap.c:886 __alloc_contig_migrate_range at mm/page_alloc.c:9078 isolate_single_pageblock at mm/page_isolation.c:405 start_isolate_page_range offline_pages memory_subsys_offline device_offline online_store dev_attr_store sysfs_kf_write kernfs_fop_write_iter new_sync_write vfs_write ksys_write __arm64_sys_write invoke_syscall el0_svc_common.constprop.0 do_el0_svc el0_svc el0t_64_sync_handler el0t_64_sync For full disclosure, I have also reverted the commit 0d523026abd4 ("mm/page_alloc: fix tracepoint mm_page_alloc_zone_locked()"), so the series can be reverted cleanly. But, I can't see how the commit 0d523026abd4 could cause this issue at all.