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 X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 71E35160A325 for ; Mon, 30 Jul 2018 15:03:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0F19B20870 for ; Mon, 30 Jul 2018 15:03:35 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0F19B20870 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731760AbeG3Qi5 (ORCPT ); Mon, 30 Jul 2018 12:38:57 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:51710 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726961AbeG3Qi5 (ORCPT ); Mon, 30 Jul 2018 12:38:57 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 1E3827DAC2; Mon, 30 Jul 2018 15:03:32 +0000 (UTC) Received: from [10.36.117.179] (ovpn-117-179.ams2.redhat.com [10.36.117.179]) by smtp.corp.redhat.com (Postfix) with ESMTP id 96691201E1C5; Mon, 30 Jul 2018 15:03:27 +0000 (UTC) Subject: Re: [PATCH v1] mm: inititalize struct pages when adding a section To: Michal Hocko Cc: Pavel Tatashin , Linux Memory Management List , LKML , gregkh@linuxfoundation.org, mingo@kernel.org, Andrew Morton , dan.j.williams@intel.com, jack@suse.cz, mawilcox@microsoft.com, jglisse@redhat.com, Souptick Joarder , kirill.shutemov@linux.intel.com, Vlastimil Babka , osalvador@techadventures.net, yasu.isimatu@gmail.com, malat@debian.org, Mel Gorman , iamjoonsoo.kim@lge.com References: <20180727165454.27292-1-david@redhat.com> <20180730113029.GM24267@dhcp22.suse.cz> <6cc416e7-522c-a67e-2706-f37aadff084f@redhat.com> <20180730120529.GN24267@dhcp22.suse.cz> <7b58af7b-5187-2c76-b458-b0f49875a1fc@redhat.com> <56e97799-fbe1-9546-46ab-a9b8ee8794e0@redhat.com> <20180730141058.GV24267@dhcp22.suse.cz> <80641d1a-72fe-26b2-7927-98fcac5e5d71@redhat.com> <20180730145035.GY24267@dhcp22.suse.cz> From: David Hildenbrand Openpgp: preference=signencrypt Autocrypt: addr=david@redhat.com; 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Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0 MIME-Version: 1.0 In-Reply-To: <20180730145035.GY24267@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.78 on 10.11.54.6 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.2]); Mon, 30 Jul 2018 15:03:32 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.2]); Mon, 30 Jul 2018 15:03:32 +0000 (UTC) for IP:'10.11.54.6' DOMAIN:'int-mx06.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'david@redhat.com' RCPT:'' Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 30.07.2018 16:50, Michal Hocko wrote: > On Mon 30-07-18 16:42:27, David Hildenbrand wrote: >> On 30.07.2018 16:10, Michal Hocko wrote: >>> On Mon 30-07-18 15:51:45, David Hildenbrand wrote: >>>> On 30.07.2018 15:30, Pavel Tatashin wrote: >>> [...] >>>>> Hi David, >>>>> >>>>> Have you figured out why we access struct pages during hot-unplug for >>>>> offlined memory? Also, a panic trace would be useful in the patch. >>>> >>>> __remove_pages() needs a zone as of now (e.g. to recalculate if the zone >>>> is contiguous). This zone is taken from the first page of memory to be >>>> removed. If the struct pages are uninitialized that value is random and >>>> we might even get an invalid zone. >>>> >>>> The zone is also used to locate pgdat. >>>> >>>> No stack trace available so far, I'm just reading the code and try to >>>> understand how this whole memory hotplug/unplug machinery works. >>> >>> Yes this is a mess (evolution of the code called otherwise ;) [1]. >> >> So I guess I should not feel bad if I am having problems understanding >> all the details? ;) >> >>> Functionality has been just added on top of not very well thought >>> through bases. This is a nice example of it. We are trying to get a zone >>> to 1) special case zone_device 2) recalculate zone state. The first >>> shouldn't be really needed because we should simply rely on altmap. >>> Whether it is used for zone device or not. 2) shouldn't be really needed >>> if the section is offline and we can check that trivially. >>> >> >> About 2, I am not sure if this is the case and that easy. To me it looks >> more like remove_pages() fixes up things that should be done in >> offline_pages(). Especially, if the same memory was onlined/offlined to >> different zones we might be in trouble (looking at code on a very high >> level view). > > Well, this might be possible. Hotplug remove path was on my todo list > for a long time. I didn't get that far TBH. shrink_zone_span begs for > some attention. > So i guess we agree that the right fix for this is to not touch struct pages when removing memory, correct? -- Thanks, David / dhildenb