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Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Liu Song , Hao Peng , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260716173504.760369-1-noren@nvidia.com> <8E9B69B5-0FBA-4CE5-B737-B83AD1FE52C3@nvidia.com> Content-Language: en-US From: Nimrod Oren In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ClientProxiedBy: FR4P281CA0284.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:e6::8) To MW4PR12MB6802.namprd12.prod.outlook.com (2603:10b6:303:20f::19) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: MW4PR12MB6802:EE_|MW6PR12MB8898:EE_ X-MS-Office365-Filtering-Correlation-Id: fd5cf13e-60d7-4ec0-7b2d-08deecd664b8 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|1800799024|376014|23010399003|7416014|4143699003|22082099003|18002099003|11063799006|10067099003|56012099006; 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(you'd probably want to make this a >>> sysctl or at least a defined value of course) >> >> The approach below makes sense to me. In terms of the actual cap size, >> I asked Codex to check what possible pageblock_size and their reserved >> sizes: >> >> 1. 1MB pageblock size (s390) and 11MB per zone, >> 2. 2MB pageblock size and 22MB per zone, >> 3. 8MB pageblock size and 88MB per zone, >> 4. 16MB pageblock size and 176MB per zone, >> 5. 32MB pageblock size and 352MB per zone, >> 6. 128MB pageblock size and 1.375GB per zone, >> 7. 512MB pageblock size and 5.5GB per zone. >> >> 1GB makes sense to me. 512MB might also work. > > Yeah I felt this was a bit of a 'dumb' solution but ultimately if we are > saying 'restrict how much memory this uses to something sane' then that's > what we should just do. > > It might be a good bandaid at least for this issue which is ongoing, well > known, and painful. > > I think at 352MB per zone and 2-3 zones for 32 MiB pageblock, plus reserves > of 2*512 MiB for 512 MiB pageblock makes 1 GiB a sensible choice here > overall. It's worth noting that while users who need more headroom can simply raise min_free_kbytes further via sysctl, those who wish to lower the value can't set it persistently since set_recommended_min_free_kbytes() may raise it back to the recommended value. I think 1 GiB sounds good, but given this behavior where raising is more accessible than lowering, I wonder if we should opt for a lower value. A new sysctl for the cap could address this, but I'm not sure whether adding one would be justified.