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Fri, 24 Jan 2025 03:40:29 +0000 Message-ID: Date: Fri, 24 Jan 2025 11:40:16 +0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/7] guest_memfd: Introduce an object to manage the guest-memfd with RamDiscardManager To: Peter Xu CC: David Hildenbrand , Paolo Bonzini , =?UTF-8?Q?Philippe_Mathieu-Daud=C3=A9?= , Michael Roth , , , Williams Dan J , Peng Chao P , Gao Chao , Xu Yilun References: <20241213070852.106092-1-chenyi.qiang@intel.com> <20241213070852.106092-3-chenyi.qiang@intel.com> Content-Language: en-US From: Chenyi Qiang In-Reply-To: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: SG2PR01CA0135.apcprd01.prod.exchangelabs.com (2603:1096:4:8f::15) To DM3PR11MB8735.namprd11.prod.outlook.com (2603:10b6:0:4b::20) Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DM3PR11MB8735:EE_|BL4PR11MB8847:EE_ X-MS-Office365-Filtering-Correlation-Id: 8858bbd4-e0a0-4780-dfcf-08dd3c28d8f9 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|366016|376014; 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On 1/21/2025 11:38 PM, Peter Xu wrote: > On Tue, Jan 21, 2025 at 05:00:45PM +0800, Chenyi Qiang wrote: >>>> + >>>> + /* block size and alignment */ >>>> + uint64_t block_size; >>> >>> Can we always fetch it from the MR/ramblock? If this is needed, better add >>> some comment explaining why. >> >> The block_size is the granularity used to track the private/shared >> attribute in the bitmap. It is currently hardcoded to 4K as guest_memfd >> may manipulate the page conversion in at least 4K size and alignment. >> I think It is somewhat a variable to cache the size and can avoid many >> getpagesize() calls. > > Though qemu does it frequently.. e.g. qemu_real_host_page_size() wraps > that. So IIUC that's not a major concern, and if it's a concern maybe we > can cache it globally instead. > > OTOH, this is not a per-ramblock limitation either, IIUC. So maybe instead > of caching it per manager, we could have memory_attr_manager_get_psize() > helper (or any better name..): > > memory_attr_manager_get_psize(MemoryAttrManager *mgr) > { > /* Due to limitation of ... always notify with host psize */ > return qemu_real_host_page_size(); > } > > Then in the future if necessary, switch to: > > memory_attr_manager_get_psize(MemoryAttrManager *mgr) > { > return mgr->mr->ramblock->pagesize; > } This looks good to me. I'll change in this way. > > Thanks, >