From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760614AbbCDJEI (ORCPT ); Wed, 4 Mar 2015 04:04:08 -0500 Received: from mgwkm02.jp.fujitsu.com ([202.219.69.169]:23057 "EHLO mgwkm02.jp.fujitsu.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753860AbbCDJEE (ORCPT ); Wed, 4 Mar 2015 04:04:04 -0500 X-SecurityPolicyCheck: OK by SHieldMailChecker v2.2.3 X-SHieldMailCheckerPolicyVersion: FJ-ISEC-20140219-2 Message-ID: <54F6C809.1080709@jp.fujitsu.com> Date: Wed, 4 Mar 2015 17:53:29 +0900 From: Kamezawa Hiroyuki User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:31.0) Gecko/20100101 Thunderbird/31.4.0 MIME-Version: 1.0 To: Xishi Qiu , Gu Zheng CC: Yasuaki Ishimatsu , Andrew Morton , Tang Chen , Yinghai Lu , Linux MM , LKML , Toshi Kani , Mel Gorman , Tejun Heo , Xiexiuqi , Hanjun Guo , Li Zefan Subject: Re: node-hotplug: is memset 0 safe in try_offline_node()? References: <54F52ACF.4030103@huawei.com> <54F58AE3.50101@cn.fujitsu.com> <54F66C52.4070600@huawei.com> <54F67376.8050001@huawei.com> <54F68270.5000203@cn.fujitsu.com> <54F6BC43.3000509@huawei.com> In-Reply-To: <54F6BC43.3000509@huawei.com> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 8bit X-SecurityPolicyCheck-GC: OK by FENCE-Mail X-TM-AS-MML: disable Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2015/03/04 17:03, Xishi Qiu wrote: > On 2015/3/4 11:56, Gu Zheng wrote: > >> Hi Xishi, >> On 03/04/2015 10:52 AM, Xishi Qiu wrote: >> >>> On 2015/3/4 10:22, Xishi Qiu wrote: >>> >>>> On 2015/3/3 18:20, Gu Zheng wrote: >>>> >>>>> Hi Xishi, >>>>> On 03/03/2015 11:30 AM, Xishi Qiu wrote: >>>>> >>>>>> When hot-remove a numa node, we will clear pgdat, >>>>>> but is memset 0 safe in try_offline_node()? >>>>> >>>>> It is not safe here. In fact, this is a temporary solution here. >>>>> As you know, pgdat is accessed lock-less now, so protection >>>>> mechanism (RCU？) is needed to make it completely safe here, >>>>> but it seems a bit over-kill. >>>>> >>> >>> Hi Gu, >>> >>> Can we just remove "memset(pgdat, 0, sizeof(*pgdat));" ? >>> I find this will be fine in the stress test except the warning >>> when hot-add memory. >> >> As you see, it will trigger the warning in free_area_init_node(). >> Could you try the following patch? It will reset the pgdat before reuse it. >> >> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c >> index 1778628..0717649 100644 >> --- a/mm/memory_hotplug.c >> +++ b/mm/memory_hotplug.c >> @@ -1092,6 +1092,9 @@ static pg_data_t __ref *hotadd_new_pgdat(int nid, u64 start) >> return NULL; >> >> arch_refresh_nodedata(nid, pgdat); >> + } else { >> + /* Reset the pgdat to reuse */ >> + memset(pgdat, 0, sizeof(*pgdat)); >> } > > Hi Gu, > > If schedule last a long time, next_zone may be still access the pgdat here, > so it is not safe enough, right? > How about just reseting pgdat->nr_zones and pgdat->classzone_idx to be 0 rather than memset() ? It seems breaking pointer information in pgdat is not a choice. Just proper "values" should be reset. Thanks, -Kame