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 lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 2947DECAAD3 for ; Fri, 9 Sep 2022 04:50:38 +0000 (UTC) Received: from localhost ([::1]:39540 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1oWVyP-0005t5-7G for qemu-devel@archiver.kernel.org; Fri, 09 Sep 2022 00:50:37 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:60688) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1oWVwc-00057A-9p for qemu-devel@nongnu.org; Fri, 09 Sep 2022 00:48:46 -0400 Received: from ams.source.kernel.org ([2604:1380:4601:e00::1]:39120) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1oWVwa-0006zq-6g for qemu-devel@nongnu.org; Fri, 09 Sep 2022 00:48:45 -0400 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 64F2EB822A8; Fri, 9 Sep 2022 04:48:40 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 77FD9C433C1; Fri, 9 Sep 2022 04:48:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1662698919; bh=0J6ER8fnpFHY39WsvpWQrzmPphu08JvaKTYLSCsE2Hg=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=Nhj471FrBLU3A3EN6xY82qO+CS7EigLtAFQjoed4e7kJlmYNbsyWx58NBcDcWid+C kpl5OUkyH4T1KLqbUBdoGbX1tHo5jzChTsJZhr63Y2a6JPOddewEf+EMoxk93bvuz9 NqGv5k6mcLo2uOReZLUpdQMNVueJVO1CH7VHOd9P1WHejMuUiLAWq1/eSAkVsNC3Fh xd5DtarFsGvOADus8UhKVpVH5D9jaRiIAJe/VLjr3kknWg2PAkKRdx+wB+RLNrdTTE S1pu4iFWorBwalJrPWhjEAwsV7cOngtqcJEVDb3sqUBFE54ruJIj9kp8cQq5SkvUdr AKq+U1uONwy/g== Message-ID: <95bd287b-d17f-fda8-58c9-20700b1e0c72@kernel.org> Date: Thu, 8 Sep 2022 21:48:35 -0700 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.12.0 Subject: Re: [PATCH v7 00/14] KVM: mm: fd-based approach for supporting KVM guest private memory Content-Language: en-US To: "Kirill A. Shutemov" , Hugh Dickins Cc: "Kirill A . Shutemov" , Chao Peng , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org, linux-doc@vger.kernel.org, qemu-devel@nongnu.org, linux-kselftest@vger.kernel.org, Paolo Bonzini , Jonathan Corbet , Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, "H . Peter Anvin" , Jeff Layton , "J . Bruce Fields" , Andrew Morton , Shuah Khan , Mike Rapoport , Steven Price , "Maciej S . Szmigiero" , Vlastimil Babka , Vishal Annapurve , Yu Zhang , jun.nakajima@intel.com, dave.hansen@intel.com, ak@linux.intel.com, david@redhat.com, aarcange@redhat.com, ddutile@redhat.com, dhildenb@redhat.com, Quentin Perret , Michael Roth , mhocko@suse.com, Muchun Song , "Gupta, Pankaj" References: <20220706082016.2603916-1-chao.p.peng@linux.intel.com> <20220818132421.6xmjqduempmxnnu2@box> <20220820002700.6yflrxklmpsavdzi@box.shutemov.name> From: Andy Lutomirski In-Reply-To: <20220820002700.6yflrxklmpsavdzi@box.shutemov.name> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=2604:1380:4601:e00::1; envelope-from=luto@kernel.org; helo=ams.source.kernel.org X-Spam_score_int: -102 X-Spam_score: -10.3 X-Spam_bar: ---------- X-Spam_report: (-10.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-3.142, RCVD_IN_DNSWL_HI=-5, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 8/19/22 17:27, Kirill A. Shutemov wrote: > On Thu, Aug 18, 2022 at 08:00:41PM -0700, Hugh Dickins wrote: >> On Thu, 18 Aug 2022, Kirill A . Shutemov wrote: >>> On Wed, Aug 17, 2022 at 10:40:12PM -0700, Hugh Dickins wrote: >>>> >>>> If your memory could be swapped, that would be enough of a good reason >>>> to make use of shmem.c: but it cannot be swapped; and although there >>>> are some references in the mailthreads to it perhaps being swappable >>>> in future, I get the impression that will not happen soon if ever. >>>> >>>> If your memory could be migrated, that would be some reason to use >>>> filesystem page cache (because page migration happens to understand >>>> that type of memory): but it cannot be migrated. >>> >>> Migration support is in pipeline. It is part of TDX 1.5 [1]. And swapping >>> theoretically possible, but I'm not aware of any plans as of now. >>> >>> [1] https://www.intel.com/content/www/us/en/developer/articles/technical/intel-trust-domain-extensions.html >> >> I always forget, migration means different things to different audiences. >> As an mm person, I was meaning page migration, whereas a virtualization >> person thinks VM live migration (which that reference appears to be about), >> a scheduler person task migration, an ornithologist bird migration, etc. >> >> But you're an mm person too: you may have cited that reference in the >> knowledge that TDX 1.5 Live Migration will entail page migration of the >> kind I'm thinking of. (Anyway, it's not important to clarify that here.) > > TDX 1.5 brings both. > > In TDX speak, mm migration called relocation. See TDH.MEM.PAGE.RELOCATE. > This seems to be a pretty bad fit for the way that the core mm migrates pages. The core mm unmaps the page, then moves (in software) the contents to a new address, then faults it in. TDH.MEM.PAGE.RELOCATE doesn't fit into that workflow very well. I'm not saying it can't be done, but it won't just work.