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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS 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 B2512C433C1 for ; Thu, 25 Mar 2021 15:13:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8730761A13 for ; Thu, 25 Mar 2021 15:13:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230475AbhCYPMm (ORCPT ); Thu, 25 Mar 2021 11:12:42 -0400 Received: from mx2.suse.de ([195.135.220.15]:47582 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230213AbhCYPMU (ORCPT ); Thu, 25 Mar 2021 11:12:20 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1616685139; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=bYQd2jiDExpwCCWc0J0FC+15FZl2RaQE8yMOzlruYlg=; b=M6UUaZFYeHrKOCFULqQgaVntMKO2mSiah71NvSeeXa1nAIJabXJp3eNy3t+XMwA1QlsGQ5 iY4h3K+lxZZPIo6tdOpxgtG1DpdNAUNCcUvOW+nHbLuRpiub+6zUEDP/EfhDi1fvNDJQic fHmPKOWdo45jXKPTRXWQFU982YXrue4= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id A6343AA55; Thu, 25 Mar 2021 15:12:19 +0000 (UTC) Date: Thu, 25 Mar 2021 16:12:19 +0100 From: Michal Hocko To: David Hildenbrand Cc: Oscar Salvador , Andrew Morton , Anshuman Khandual , Vlastimil Babka , Pavel Tatashin , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v5 1/5] mm,memory_hotplug: Allocate memmap from the added memory range Message-ID: References: <31110e58-c99a-8dee-6f6e-98f456b77759@redhat.com> <062bc5d7-a83c-1c1a-7b77-9f043643f4fa@redhat.com> <31c3e6f7-f631-7b00-2c33-518b0f24a75f@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <31c3e6f7-f631-7b00-2c33-518b0f24a75f@redhat.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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? -- Michal Hocko SUSE Labs