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dkim=none (message not signed) header.d=none;intel.com; dmarc=none action=none header.from=amd.com; Received: from SN6PR12MB2767.namprd12.prod.outlook.com (2603:10b6:805:75::23) by SN6PR12MB2830.namprd12.prod.outlook.com (2603:10b6:805:e0::27) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4500.14; Fri, 10 Sep 2021 09:42:35 +0000 Received: from SN6PR12MB2767.namprd12.prod.outlook.com ([fe80::491e:2642:bae2:8b73]) by SN6PR12MB2767.namprd12.prod.outlook.com ([fe80::491e:2642:bae2:8b73%7]) with mapi id 15.20.4478.026; Fri, 10 Sep 2021 09:42:35 +0000 Date: Fri, 10 Sep 2021 09:42:32 +0000 From: Ashish Kalra To: "Wang, Wei W" Cc: "qemu-devel@nongnu.org" , "pbonzini@redhat.com" , "Thomas.Lendacky@amd.com" , "brijesh.singh@amd.com" , "dgilbert@redhat.com" , "ehabkost@redhat.com" , "dovmurik@linux.vnet.ibm.com" , "tobin@ibm.com" , "jejb@linux.ibm.com" Subject: Re: [PATCH v4 10/14] migration: add support to migrate shared regions list Message-ID: <20210910094232.GC2686@ashkalra_ubuntu_server> References: <9236f522e48b67fe7136de7620276f7dc193be37.1628076205.git.ashish.kalra@amd.com> <6a48e7c8b6e14933aa0085d12e2c5ff7@intel.com> <20210910084740.GA2686@ashkalra_ubuntu_server> Content-Type: text/plain; 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envelope-from=Ashish.Kalra@amd.com; helo=NAM11-DM6-obe.outbound.protection.outlook.com X-Spam_score_int: -10 X-Spam_score: -1.1 X-Spam_bar: - X-Spam_report: (-1.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, FORGED_SPF_HELO=1, MSGID_FROM_MTA_HEADER=0.001, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_PASS=-0.001, T_SPF_TEMPERROR=0.01 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 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 Fri, Sep 10, 2021 at 09:11:09AM +0000, Wang, Wei W wrote: > On Friday, September 10, 2021 4:48 PM, Ashish Kalra wrote: > > On Fri, Sep 10, 2021 at 07:54:10AM +0000, Wang, Wei W wrote: > > There has been a long discussion on this implementation on KVM mailing list. > > Tracking shared memory via a list of ranges instead of using bitmap is more > > optimal. Most of the guest memory will be private and the unencrypted/shared > > regions are basically ranges/intervals, so easy to implement and maintain using > > lists. > > OK. At which version did you discuss this or do you have a link? (I didn't find it in v9 KVM patches) > You can follow this email thread: https://lore.kernel.org/kvm/20201211225542.GA30409@ashkalra_ubuntu_server/ > > A list will consume much less memory than a bitmap. > > > > The bitmap will consume more memory as it will need to be sized as per guest > > RAM size and will remain sparsely populated due to limited amount of > > shared/unencrypted guest memory regions. > > I also thought about this. It depends on the guest. > I think "A list will consume much less memory" is true when we assume most of guest pages are private pages. > From design perspective, what if guest chooses to have most of its pages being shared? > Lists might consume much more memory than bitmaps in some cases, I think. > (Probably I can check your previous discussions first) > This will probably depend on the most common use case and scenario, i think that most common use case will be a mostly encrypted guest. Thanks, Ashish