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 8610FCD68E0 for ; Tue, 10 Oct 2023 00:42:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1379248AbjJJAmS (ORCPT ); Mon, 9 Oct 2023 20:42:18 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59640 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1379237AbjJJAmN (ORCPT ); Mon, 9 Oct 2023 20:42:13 -0400 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B1E9F9F for ; Mon, 9 Oct 2023 17:42:12 -0700 (PDT) Received: by smtp.kernel.org (Postfix) with ESMTPSA id DA6E0C433C7; Tue, 10 Oct 2023 00:41:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1696898532; bh=Jh0sIBZh8nxYbq7VHsim1Kh7Mp+jQxSntzGqnBwKMdM=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=o87WvQrd7I/dovg4pdMTbRabyl26XrcKQ0m+jND++sXRPeTn3nE4igwsAyn5wgNiX Yr/s6LBeJMB5FBRXOKggvWzX/+1pkIXQgQIJeXBIG6LxBVqf51T3yEvYVBmZsF4xiq oRbCdSydZNA7EQrMu7+Vt0QtSmlBj904i6oGEOCs= Date: Mon, 9 Oct 2023 17:41:35 -0700 From: Andrew Morton To: Huang Ying Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Christoph Lameter , Mel Gorman , Vlastimil Babka , Michal Hocko Subject: Re: [PATCH -V2] mm: fix draining PCP of remote zone Message-Id: <20231009174135.2357dcfcdc691a6ef61dbd9a@linux-foundation.org> In-Reply-To: <20231007062356.187621-1-ying.huang@intel.com> References: <20231007062356.187621-1-ying.huang@intel.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 7 Oct 2023 14:23:56 +0800 Huang Ying wrote: > If there is no memory allocation/freeing in the PCP (Per-CPU Pageset) > of a remote zone (zone in remote NUMA node) after some time (3 seconds > for now), the pages of the PCP of the remote zone will be drained to > avoid memory wastage. > > This behavior was introduced in the commit 4ae7c03943fc ("[PATCH] > Periodically drain non local pagesets") and the commit > 4037d452202e ("Move remote node draining out of slab allocators") > > But, after the commit 7cc36bbddde5 ("vmstat: on-demand vmstat workers > V8"), the vmstat updater worker which is used to drain the PCP of > remote zones may not be re-queued when we are waiting for the > timeout (pcp->expire != 0) if there are no vmstat changes on this CPU, > for example, when the CPU goes idle or runs user space only workloads. > This may cause the pages of a remote zone be kept in PCP of this CPU > for long time. So that, the page reclaiming of the remote zone may be > triggered prematurely. This isn't a severe problem in practice, > because the PCP of the remote zone will be drained if some memory are > allocated/freed again on this CPU. And, the PCP will eventually be > drained during the direct reclaiming if necessary. > > Anyway, the problem still deserves a fix via guaranteeing that the > vmstat updater worker will always be re-queued when we are waiting for > the timeout. In effect, this restores the original behavior before > the commit 7cc36bbddde5. > > We can reproduce the bug via allocating/freeing pages from a remote > zone then go idle as follows. And the patch can fix it. > > - Run some workloads, use `numactl` to bind CPU to node 0 and memory to > node 1. So the PCP of the CPU on node 0 for zone on node 1 will be > filled. > > - After workloads finish, idle for 60s > > - Check /proc/zoneinfo > > With the original kernel, the number of pages in the PCP of the CPU on > node 0 for zone on node 1 is non-zero after idle. With the patched > kernel, it becomes 0 after idle. That is, we avoid to keep pages in > the remote PCP during idle. > Thanks, I updated the changelog in place and queued this for mm-stable.