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=-7.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 E169BC433E0 for ; Thu, 25 Mar 2021 15:20:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BE25461A1A for ; Thu, 25 Mar 2021 15:20:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231442AbhCYPUT (ORCPT ); Thu, 25 Mar 2021 11:20:19 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:47079 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231420AbhCYPTw (ORCPT ); Thu, 25 Mar 2021 11:19:52 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1616685592; 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:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=zNM38P4llzp6ono8knMMf4l95meVg1P7je5WpXvzenI=; b=J5UwpWo7jOLOrQ7FGXWiH9sMyrCuKe7kledXvVWXcSGtmdijvg1r7GMz+hKbz3wCEW/Rl4 7tvJ3zoxCKIUhfcujK9LP5j48ea5OoYhHbmQ5i6OcIP8D7385HFVxK3pSa56mQIZWpdXA7 yXc5PLtJ++g8mE1PTS+H+6GggPV5NoE= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-347-i3XBKAS7Ma-Ycwq7hufBWg-1; Thu, 25 Mar 2021 11:19:50 -0400 X-MC-Unique: i3XBKAS7Ma-Ycwq7hufBWg-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 755A48BEF5D; Thu, 25 Mar 2021 15:19:39 +0000 (UTC) Received: from [10.36.115.72] (ovpn-115-72.ams2.redhat.com [10.36.115.72]) by smtp.corp.redhat.com (Postfix) with ESMTP id 2CDD25C3DF; Thu, 25 Mar 2021 15:19:36 +0000 (UTC) Subject: Re: [PATCH v5 1/5] mm,memory_hotplug: Allocate memmap from the added memory range To: Michal Hocko Cc: Oscar Salvador , Andrew Morton , Anshuman Khandual , Vlastimil Babka , Pavel Tatashin , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <31110e58-c99a-8dee-6f6e-98f456b77759@redhat.com> <062bc5d7-a83c-1c1a-7b77-9f043643f4fa@redhat.com> <31c3e6f7-f631-7b00-2c33-518b0f24a75f@redhat.com> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: <40fac999-2d28-9205-23f0-516fa9342bbe@redhat.com> Date: Thu, 25 Mar 2021 16:19:36 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 25.03.21 16:12, Michal Hocko wrote: > On Thu 25-03-21 15:46:22, David Hildenbrand wrote: >> On 25.03.21 15:34, Michal Hocko wrote: >>> On Thu 25-03-21 15:09:35, David Hildenbrand wrote: >>>> On 25.03.21 15:08, Michal Hocko wrote: >>>>> On Thu 25-03-21 13:40:45, David Hildenbrand wrote: >>>>>> On 25.03.21 13:35, Michal Hocko wrote: >>>>>>> On Thu 25-03-21 12:08:43, David Hildenbrand wrote: >>>>>>>> On 25.03.21 11:55, Oscar Salvador wrote: >>>>> [...] >>>>>>>>> - When moving the initialization/accounting to hot-add/hot-remove, >>>>>>>>> the section containing the vmemmap pages will remain offline. >>>>>>>>> It might get onlined once the pages get online in online_pages(), >>>>>>>>> or not if vmemmap pages span a whole section. >>>>>>>>> I remember (but maybe David rmemeber better) that that was a problem >>>>>>>>> wrt. pfn_to_online_page() and hybernation/kdump. >>>>>>>>> So, if that is really a problem, we would have to care of ot setting >>>>>>>>> the section to the right state. >>>>>>>> >>>>>>>> Good memory. Indeed, hibernation/kdump won't save the state of the vmemmap, >>>>>>>> because the memory is marked as offline and, thus, logically without any >>>>>>>> valuable content. >>> >>> ^^^^ THIS >>> >>>>>>> >>>>>>> Could you point me to the respective hibernation code please? I always >>>>>>> get lost in that area. Anyway, we do have the same problem even if the >>>>>>> whole accounting is handled during {on,off}lining, no? >>>>>> >>>>>> kernel/power/snapshot.c:saveable_page(). >>>>> >>>>> Thanks! So this is as I've suspected. The very same problem is present >>>>> if the memory block is marked offline. So we need a solution here >>>>> anyway. One way to go would be to consider these vmemmap pages always >>>>> online. pfn_to_online_page would have to special case them but we would >>>>> need to identify them first. I used to have PageVmemmap or something >>>>> like that in my early attempt to do this. >>>>> >>>>> That being said this is not an argument for one or the other aproach. >>>>> Both need fixing. >>>> >>>> Can you elaborate? What is the issue there? What needs fixing? >>> >>> offline section containing vmemmap will be lost during hibernation cycle >>> IIU the above correctly. >>> >> >> Can tell me how that is a problem with Oscars current patch? I only see this >> being a problem with what you propose - most probably I am missing something >> important here. >> >> Offline memory sections don't have a valid memmap (assumption: garbage). On >> hibernation, the whole offline memory block won't be saved, including the >> vmemmap content that resides on the block. This includes the vmemmap of the >> vmemmap pages, which is itself. >> >> When restoring, the whole memory block will contain garbage, including the >> whole vmemmap - which is marked to be offline and to contain garbage. > > Hmm, so I might be misunderstanding the restoring part. But doesn't that > mean that the whole section/memory block won't get restored because it > is offline and therefore the vmemmap would be pointing to nowhere? AFAIU, only the content of the memory block won't be restored - whatever memory content existed before the restore operation is kept. The structures that define how the vmemmap should look like - the memory sections and the page tables used for describing the vmemmap should properly get saved+restored, as these are located on online memory. So the vmemmap layout should look after restoring just like before saving. -- Thanks, David / dhildenb