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Howlett" , "Nico Pache" , "Ryan Roberts" , "Dev Jain" , "Barry Song" , "Lance Yang" , "Usama Arif" , "Kiryl Shutsemau" , "Mike Rapoport" , "Suren Baghdasaryan" , "Michal Hocko" , "Brendan Jackman" , "Johannes Weiner" , "Hugh Dickins" , "Nirmoy Das" , "Dragos Tatulea" , , To: "Johannes Weiner" , "Vlastimil Babka (SUSE)" , "Nimrod Oren" , "Andrew Morton" , "David Hildenbrand" , "Lorenzo Stoakes" From: "Zi Yan" X-Mailer: aerc 0.22.0 References: <20260901190123.3511535-1-noren@nvidia.com> In-Reply-To: X-ClientProxiedBy: YQBPR0101CA0203.CANPRD01.PROD.OUTLOOK.COM (2603:10b6:c01:67::11) To IA0PR12MB8374.namprd12.prod.outlook.com (2603:10b6:208:40e::7) 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: IA0PR12MB8374:EE_|PH7PR12MB5594:EE_ X-MS-Office365-Filtering-Correlation-Id: b6e8e776-08a1-4486-e648-08df0da427ed X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|23010399003|7416014|376014|1800799024|13003099007|10067099003|11063799006|4143699003|56012099006|18002099003|22082099003; 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With the >> default arm64 pageblock sizes, the contribution per eligible zone >> before applying the existing cap of 5% of low memory is: >>=20 >> 4 KiB pages: 2 MiB pageblock, 22 MiB per zone >> 16 KiB pages: 32 MiB pageblock, 352 MiB per zone >> 64 KiB pages: 512 MiB pageblock, 5.5 GiB per zone >>=20 >> Even with that cap, min_free_kbytes can reach excessive levels. >>=20 >> The automatic min_free_kbytes increase predates proactive compaction >> and many subsequent changes to compaction. Given those changes, >> increasing min_free_kbytes for THP by default is no longer clearly >> justified. >>=20 >> Remove set_recommended_min_free_kbytes() and all associated >> recalculation paths. With this policy gone, min_free_kbytes is >> controlled only by the page allocator's default calculation and the >> vm.min_free_kbytes sysctl. Users who want additional headroom may set a >> higher value via that sysctl. >>=20 >> Link: https://lore.kernel.org/r/20260831075635.2244437-1-noren@nvidia.co= m/ >> Suggested-by: Michal Hocko >> Signed-off-by: Nimrod Oren >> --- >> v3: >> * Replace the 1 GiB cap with removal of the THP-driven min_free_kbytes >> increase as suggested by Michal. >> * Remove all associated recalculation paths. >> * Make min_free_kbytes, user_min_free_kbytes, >> calculate_min_free_kbytes(), and setup_per_zone_wmarks() static. >> * Drop the now-unused declarations and khugepaged's page_alloc.h include= . >> * Drop the obsolete v2 documentation addition. >>=20 >> v2: >> * Use a named constant for the cap. >> * Drop explicit linux/sizes.h include. >> * Update min_free_kbytes documentation. >> https://lore.kernel.org/r/20260831075635.2244437-1-noren@nvidia.com/ >>=20 >> v1: >> * Cap the final recommendation at 1 GiB as suggested by Lorenzo. >> https://lore.kernel.org/r/20260728202014.2517142-1-noren@nvidia.com/ >>=20 >> RFC v1: >> https://lore.kernel.org/r/20260716173504.760369-1-noren@nvidia.com/ >> --- >> include/linux/khugepaged.h | 5 ---- >> mm/huge_memory.c | 14 --------- >> mm/internal.h | 8 ----- >> mm/khugepaged.c | 60 -------------------------------------- >> mm/page_alloc.c | 11 +++---- >> mm/page_alloc.h | 2 -- >> mm/shmem.c | 7 ----- >> 7 files changed, 4 insertions(+), 103 deletions(-) > > Given neither of the patchset versions achieved universal acceptance, cou= ld > we try just disabling all the automatic (re)calculations of min_free_kbyt= es > the first moment the sysctl gets adjusted from userspace? Sounds good to me. Johannes, WDYT? --=20 Best Regards, Yan, Zi