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Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Shuah Khan , linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org Subject: Re: [RFC PATCH 02/11] mm/khugepaged: remove READ_ONLY_THP_FOR_FS code in collapse_file() Date: Mon, 23 Mar 2026 20:12:42 -0400 X-Mailer: MailMate (2.0r6290) Message-ID: In-Reply-To: <16117b49-d83d-4ceb-b85d-d117d6993ce1@kernel.org> References: <20260323190644.1714379-1-ziy@nvidia.com> <20260323190644.1714379-3-ziy@nvidia.com> <7382046f-7c58-4a3e-ab34-b2704355b7d5@kernel.org> <71148f2e-cceb-418e-b762-c8dbd7a7eb1f@kernel.org> <9648838a-ada7-4983-99e3-d694e803e06b@kernel.org> <16117b49-d83d-4ceb-b85d-d117d6993ce1@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-ClientProxiedBy: MN2PR14CA0005.namprd14.prod.outlook.com (2603:10b6:208:23e::10) To DS7PR12MB9473.namprd12.prod.outlook.com (2603:10b6:8:252::5) 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: DS7PR12MB9473:EE_|BY5PR12MB4130:EE_ X-MS-Office365-Filtering-Correlation-Id: e1271589-29ad-4d26-df94-08de893a12f5 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|7416014|376014|366016|56012099003|22082099003|18002099003; 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if you set VM_HUGEPAGE, >>>> do_sync_mmap_readahead() will allocate PMD-sized folios automatically. >>>> On busy database servers (and is there any other kind?), khugepaged >>>> takes too long to run and find opportunities to collapse text pages. >>>> Like, days. >>> >>> Yes, in particular given that the default khugepaged settings are awful. >>> >>>> >>>> >>>> I think the test needs to be: >>>> >>>> if (mapping_max_folio_order(mapping) >= PMD_ORDER) >> >> This is very helpful, since I was thinking about using >> mapping_large_folio_support(). >> >>>> >>>> as there can be cases of filesystems which support up to, say, 64KiB, >>>> but not all the way up to 2MiB. I disapprove of this situation, but >>>> this is where we are right now. >>> >>> Right, that's what I had in mind. >> >> Does Nico’s mTHP support for khugepaged include changes to collapse_file()? >> That might change the above test. > > At least not regarding adding support for other folio sizes. Baolin > (IIRC) had a version for shmem support, but that will come after Nico's > series was merged. Great. That makes my life easier. Thanks. Best Regards, Yan, Zi