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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6F5EEECAAA1 for ; Fri, 9 Sep 2022 04:48:43 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 0AC968D0003; Fri, 9 Sep 2022 00:48:43 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 05CCC8D0002; Fri, 9 Sep 2022 00:48:43 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E67A68D0003; Fri, 9 Sep 2022 00:48:42 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id D93E38D0002 for ; Fri, 9 Sep 2022 00:48:42 -0400 (EDT) Received: from smtpin25.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay04.hostedemail.com (Postfix) with ESMTP id BC02B1A080D for ; Fri, 9 Sep 2022 04:48:42 +0000 (UTC) X-FDA: 79891316484.25.4D77FDF Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by imf31.hostedemail.com (Postfix) with ESMTP id 4C19B20095 for ; Fri, 9 Sep 2022 04:48:42 +0000 (UTC) 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 ARC-Authentication-Results: i=1; imf31.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=Nhj471Fr; dmarc=pass (policy=none) header.from=kernel.org; spf=pass (imf31.hostedemail.com: domain of luto@kernel.org designates 145.40.68.75 as permitted sender) smtp.mailfrom=luto@kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1662698922; a=rsa-sha256; cv=none; b=uSFYGFCeM0dyb0zkjkOiQzah9UoCESxZh1kUDzT8FpX31raNqV767UHj4bbqismK2ta7tf UJXoQb309RNdk7s0eXlISTnVz+wXeagqnsNN6XVovfKQwSTntxA7WgDF9e+d9tV5QQ+G/c tr9N+/aUoLW1xd8VVH/vgGbfhOLZ0/Q= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1662698922; h=from:from:sender: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:dkim-signature; bh=PcSN9ShMcdae25z0ncAl7z4QQzYQwQoHD/MixpB3OUs=; b=3a6hZWp2dEVlcp6YYcO+rUV3r5zSkZTjISaPPfzl6M+ETjnWl1iAKiL6mWf7ZU0KLyt7Oc zV7naioU2ptkdnz78m73z3mCMHNRA4rP8u9LGnm1osMKsgHGcntn9bY2U6pJN3Vx2y1s+w 8n8+4dn0nclM7+pNYN8apwveAKO2zfg= Authentication-Results: imf31.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=Nhj471Fr; dmarc=pass (policy=none) header.from=kernel.org; spf=pass (imf31.hostedemail.com: domain of luto@kernel.org designates 145.40.68.75 as permitted sender) smtp.mailfrom=luto@kernel.org X-Rspam-User: X-Rspamd-Server: rspam01 X-Stat-Signature: mnz5zfesyw6x55jykuu6c64qm7qmo1p8 X-Rspamd-Queue-Id: 4C19B20095 X-HE-Tag: 1662698922-407871 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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.