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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 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 xBSioHP/ j7/yCJiysJO/PGlfhL+tc168zsW5ipSUgAH95inkns7A34KnozN3twSoSsNO5w7JSRpZ939x5WCsMaOvxTuppmqcY1JUqZBn+SpxaRCJshEih4Bb2AuIZ0xuoV0m/YpcVVgmObYVoWBTusW91pYDrhCDapVlwAg9yYbaRg5IrNl5Aifr/Pk84Ao0DMzCydTXCsqNeDDdJWaBZ+jM0CJCk78ga7QC3ByLLMPeeClGKidXqAJQMOxFEDDfPq5qvrRV2V16Efx9lujofoCM36CsacajoLaVlQkvqB0Ms0Ci9KT/dOwBzYtNNNLj4pxtANPeEq+tbwtgc2QsIF8Qs/jmiuNioblGE+gY+vbYHPCZaL6f5Khr5OZ+6ZUKKO3E1+jl4lca/DNJx2dNNyUejU9hlsTddvWoQ+mlWJKbLrLIT9MKv3Ic+E1gxejl6Ka1RP2Guy0JG Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 23 Mar 2026, at 17:21, David Hildenbrand (Arm) wrote: > On 3/23/26 22:11, Zi Yan wrote: >> On 23 Mar 2026, at 17:05, David Hildenbrand (Arm) wrote: >> >>> On 3/23/26 22:02, Matthew Wilcox wrote: >>>> >>>> Not necessarily that lucky; 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