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Mon, 29 Dec 2025 20:55:04 -0600 Received: from [10.65.99.138] (10.180.168.240) by satlexmb07.amd.com (10.181.42.216) with Microsoft SMTP Server id 15.2.2562.17 via Frontend Transport; Mon, 29 Dec 2025 18:55:02 -0800 Message-ID: <8123efd8-73cc-4dfa-9f1e-6d9a95f66984@amd.com> Date: Tue, 30 Dec 2025 10:55:02 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 0/1] numa: add 'spm' option for Specific Purpose Memory To: Gregory Price CC: , , , , , References: <20251209093841.2250527-1-FangSheng.Huang@amd.com> From: "Huang, FangSheng (Jerry)" In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: None (SATLEXMB04.amd.com: FangSheng.Huang@amd.com does not designate permitted sender hosts) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CO1PEPF000066E7:EE_|DM4PR12MB6181:EE_ X-MS-Office365-Filtering-Correlation-Id: 8d3999cc-94eb-4174-a443-08de474ed67f X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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On 12/30/2025 2:26 AM, Gregory Price wrote: > On Tue, Dec 09, 2025 at 05:38:40PM +0800, fanhuang wrote: >> Example usage: >> -object memory-backend-ram,size=8G,id=m0 >> -object memory-backend-file,size=8G,id=m1,mem-path=/dev/dax0.0 >> -numa node,nodeid=0,memdev=m0 >> -numa node,nodeid=1,memdev=m1,spm=on >> > > Interesting that you added spm= to NUMA rather than the memory backend, > but then in the patch you consume it to apply to the EFI/E820 memory > maps. > > Sorry i've missed prior versions, is numa the right place to put this, > considering that the node is not necessarily 100% SPM on a real system? > The decision to add `spm=` to NUMA rather than the memory backend was based on earlier feedback from David during our initial RFC discussions. David raised a concern that if we put the spm flag on the memory backend, a user could accidentally pass such a memory backend to DIMM/virtio-mem/boot memory, which would have very undesired side effects. > (in practice it should be, but not technically required to be) You're right that on a real system, a NUMA node is not technically required to be 100% SPM. However, in AMD's use case, the entire NUMA node memory (backed by memdev) is intended to be SPM, and this approach provides a cleaner and safer configuration interface. > > ~Gregory Please let me know if you have further concerns or suggestions. Best Regards, Jerry Huang