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Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Vlastimil Babka References: <20260728202014.2517142-1-noren@nvidia.com> <20260728171710.a968591ceea5782270dffcee@linux-foundation.org> Content-Language: en-US From: Nimrod Oren In-Reply-To: <20260728171710.a968591ceea5782270dffcee@linux-foundation.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ClientProxiedBy: FR4P281CA0223.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:e4::6) 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_|SA3PR12MB9089:EE_ X-MS-Office365-Filtering-Correlation-Id: 00cae3b6-2b67-4e89-3750-08def1f8c5d8 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|7416014|376014|1800799024|23010399003|366016|56012099006|11063799006|10067099003|4143699003|18002099003|22082099003; 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This bounds the automatic recommendation to a >> sane value on systems with large pageblocks while preserving existing >> behavior for typical systems with 2 MiB pageblocks. > > Another hard-coded number isn't pretty :( The 1 GiB value follows the RFC discussion. Would a dedicated constant (e.g. THP_MIN_FREE_MAX_PAGES) make it better? Would using a new sysctl be preferable? >> diff --git a/mm/khugepaged.c b/mm/khugepaged.c >> index 27e8f3077e80..d9caf10e05b5 100644 >> --- a/mm/khugepaged.c >> +++ b/mm/khugepaged.c >> @@ -23,6 +23,7 @@ >> #include >> #include >> #include >> +#include > > Why this? For SZ_1G. It's already included transitively, so I'll drop it in the next revision. >> #include >> #include "internal.h" >> @@ -3096,9 +3097,13 @@ void set_recommended_min_free_kbytes(void) >> recommended_min += pageblock_nr_pages * nr_zones * >> MIGRATE_PCPTYPES * MIGRATE_PCPTYPES; >> >> - /* don't ever allow to reserve more than 5% of the lowmem */ >> + /* >> + * Don't ever allow to reserve more than 5% of lowmem or 1 GiB, >> + * whichever is smaller. >> + */ >> recommended_min = min(recommended_min, >> (unsigned long) nr_free_buffer_pages() / 20); >> + recommended_min = min(recommended_min, SZ_1G / PAGE_SIZE); >> recommended_min <<= (PAGE_SHIFT-10); >> >> if (recommended_min > min_free_kbytes) { > > Is a min_free_kbytes documentation update needed? > Documentation/admin-guide/sysctl/vm.rst. I can document THP's automatic recommendation there in the next revision, along with whichever capping mechanism we decide on. Thanks for the review!