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 3BF84C433EF for ; Thu, 14 Jul 2022 05:14:03 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 948A1940189; Thu, 14 Jul 2022 01:14:02 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 8F6DD940134; Thu, 14 Jul 2022 01:14:02 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 74B62940189; Thu, 14 Jul 2022 01:14:02 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id 63A9B940134 for ; Thu, 14 Jul 2022 01:14:02 -0400 (EDT) Received: from smtpin14.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 2CB4E20639 for ; Thu, 14 Jul 2022 05:14:02 +0000 (UTC) X-FDA: 79684538724.14.1028885 Received: from NAM10-BN7-obe.outbound.protection.outlook.com (mail-bn7nam10on2059.outbound.protection.outlook.com [40.107.92.59]) by imf22.hostedemail.com (Postfix) with ESMTP id 697C0C0078 for ; Thu, 14 Jul 2022 05:14:01 +0000 (UTC) ARC-Seal: i=1; a=rsa-sha256; s=arcselector9901; d=microsoft.com; cv=none; b=konCyrcv1WTttlX98x1x4ibySLYZ9wQSiW28Wm9Wvgtym2DKnikFoYLRpNCE3ajZdlaMbHwlH18XnMlHKhqReiRNeP4gpwIieOXQ6C7M8yos1TbXLrzj0GKp3EVUf8j55NjC5o9YaCC1RERwuOpTiAGD37RWwyAwvTrBiw92o5N1l9lMw0V+NtmrRsBBX1RJmO95l/0lgDNqaaGmwslCwmlrho9X5P2g8V2hus2bOU/r1W9sWM95hSzrCILZWDLiOgpIIw7ay43lZAaJ6VowhXwHcedznlEDTc8sQ5B2a9FLGiKTDPBaedVyaBVHsFE/BSjakc1NgjIT8+qV9TrLpQ== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=microsoft.com; s=arcselector9901; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-AntiSpam-MessageData-ChunkCount:X-MS-Exchange-AntiSpam-MessageData-0:X-MS-Exchange-AntiSpam-MessageData-1; bh=hD6U9IBmIvIpZco/ZjWYvMR6AW/yL3LBjjbeei/n1Fg=; b=YOWWOO0aLtPmACS0HhXe7Xw7k9NpQjF5wT9ol3xgY9n5KRB2erqQeQary01l0fRipxLFCOs7OkifHp3euF/2G7U7lO2qBJ0iXcUsXbUSYVzyrax0RaKv0Ept5/df2jpr8DNad8POvSJogexnbLF85/QpTgHq1yRa2NS7uefdkGs0zFcg52NQNTQgGHPoXM0OBu71kWMWbYnodiR8w6k2zrD03yLtJUgUz7UENsaOETLiiJeRrmcmQ+9L+YvkbV0HIApPksY5HwfUZm9sLG4vx8u3ajJSNNhT0/NI8BOCu4TKZksoUyFJm7Cj2/0J6+GHSNYpKTFD+56E1B43kkJjjw== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=amd.com; dmarc=pass action=none header.from=amd.com; dkim=pass header.d=amd.com; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amd.com; s=selector1; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=hD6U9IBmIvIpZco/ZjWYvMR6AW/yL3LBjjbeei/n1Fg=; b=Nj4tza8y8R+6LS9mn6xgNUM9+y+xAdj/FmdxMHvRKvb9kN/22XlyTzzrEKoU3MrE87/ZWzeuQhl6DNf8bDvV+j+ahpOb4/d3AuL831sRFc8tZjl0DqaqpU2slofBToDEwYIy6LV+ME6V1c9tBqYMT2AzrSuz2v7RPo21P1LABKk= Received: from CY4PR1201MB0181.namprd12.prod.outlook.com (2603:10b6:910:1f::11) by MWHPR1201MB0125.namprd12.prod.outlook.com (2603:10b6:301:55::12) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.5417.23; Thu, 14 Jul 2022 05:13:58 +0000 Received: from CY4PR1201MB0181.namprd12.prod.outlook.com ([fe80::1001:3c79:9504:8d6a]) by CY4PR1201MB0181.namprd12.prod.outlook.com ([fe80::1001:3c79:9504:8d6a%10]) with mapi id 15.20.5417.026; Thu, 14 Jul 2022 05:13:58 +0000 Message-ID: <1ea62889-1919-bee9-2314-68ead1e72f06@amd.com> Date: Thu, 14 Jul 2022 07:13:45 +0200 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.10.0 Subject: Re: [PATCH v7 00/14] KVM: mm: fd-based approach for supporting KVM guest private memory Content-Language: en-US To: Andy Lutomirski , Chao Peng Cc: kvm list , Linux Kernel Mailing List , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, Linux API , 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 , the arch/x86 maintainers , "H. Peter Anvin" , Hugh Dickins , Jeff Layton , "J . Bruce Fields" , Andrew Morton , Shuah Khan , Mike Rapoport , Steven Price , "Maciej S . Szmigiero" , Vlastimil Babka , Vishal Annapurve , Yu Zhang , "Kirill A. Shutemov" , "Nakajima, Jun" , Dave Hansen , Andi Kleen , David Hildenbrand , aarcange@redhat.com, ddutile@redhat.com, dhildenb@redhat.com, Quentin Perret , Michael Roth , Michal Hocko , Muchun Song References: <20220706082016.2603916-1-chao.p.peng@linux.intel.com> <20220713075738.GC2831541@chaop.bj.intel.com> <13d25d2e-ff79-5762-ddb8-87df56f5cbcf@amd.com> From: "Gupta, Pankaj" In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: FR3P281CA0141.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:95::14) To CY4PR1201MB0181.namprd12.prod.outlook.com (2603:10b6:910:1f::11) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 645cd842-6567-4380-cfb1-08da6557a7d2 X-MS-TrafficTypeDiagnostic: MWHPR1201MB0125:EE_ X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:CY4PR1201MB0181.namprd12.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230016)(4636009)(346002)(136003)(39860400002)(396003)(366004)(376002)(5660300002)(54906003)(6486002)(6506007)(478600001)(2906002)(316002)(6666004)(31686004)(26005)(41300700001)(6512007)(110136005)(36756003)(31696002)(2616005)(38100700002)(4326008)(66556008)(7416002)(8676002)(7406005)(86362001)(8936002)(186003)(66476007)(66946007)(43740500002)(45980500001);DIR:OUT;SFP:1101; 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b=5Qby7iPD98ECR1Hd1VVOioVnFB9x1XAu8e0HA5Dxz01gD/j7bOjwtYCRhbimTxHNCNgRT0 a7rq7E9mFyykwVCzv4AWmiJyB8LngOmbkqF25cRdivY/zHZ3DgmpSy58/gJTLOy+JTYJom wUYLNzok+N9KL/VBmsNAplwl1kd5o70= Authentication-Results: imf22.hostedemail.com; dkim=pass header.d=amd.com header.s=selector1 header.b=Nj4tza8y; dmarc=pass (policy=quarantine) header.from=amd.com; arc=pass ("microsoft.com:s=arcselector9901:i=1"); spf=pass (imf22.hostedemail.com: domain of Pankaj.Gupta@amd.com designates 40.107.92.59 as permitted sender) smtp.mailfrom=Pankaj.Gupta@amd.com X-Rspam-User: X-Stat-Signature: hdsrenh9cym86b64z6epeu83cac8zbaq X-Rspamd-Queue-Id: 697C0C0078 X-Rspamd-Server: rspam08 X-HE-Tag: 1657775641-909432 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: >>>>> This is the v7 of this series which tries to implement the fd-based KVM >>>>> guest private memory. The patches are based on latest kvm/queue branch >>>>> commit: >>>>> >>>>> b9b71f43683a (kvm/queue) KVM: x86/mmu: Buffer nested MMU >>>>> split_desc_cache only by default capacity >>>>> >>>>> Introduction >>>>> ------------ >>>>> In general this patch series introduce fd-based memslot which provides >>>>> guest memory through memory file descriptor fd[offset,size] instead of >>>>> hva/size. The fd can be created from a supported memory filesystem >>>>> like tmpfs/hugetlbfs etc. which we refer as memory backing store. KVM >>>> >>>> Thinking a bit, As host side fd on tmpfs or shmem will store memory on host >>>> page cache instead of mapping pages into userspace address space. Can we hit >>>> double (un-coordinated) page cache problem with this when guest page cache >>>> is also used? >>> >>> This is my understanding: in host it will be indeed in page cache (in >>> current shmem implementation) but that's just the way it allocates and >>> provides the physical memory for the guest. In guest, guest OS will not >>> see this fd (absolutely), it only sees guest memory, on top of which it >>> can build its own page cache system for its own file-mapped content but >>> that is unrelated to host page cache. >> >> yes. If guest fills its page cache with file backed memory, this at host >> side(on shmem fd backend) will also fill the host page cache fast. This >> can have an impact on performance of guest VM's if host goes to memory >> pressure situation sooner. Or else we end up utilizing way less System >> RAM. > > Is this in any meaningful way different from a regular VM? After thinking a bit, Seems 'No'. Except the reclaim decisions system would take under memory pressure and also will have to see how well this gets stitched with memory tiers in future. But all these are future topics. Sorry! for the noise. Thanks, Pankaj