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[PATCH 0/5] Fix deferred_split_isolate() and clean up __folio_freeze_and_split_unmapped() To: Kiryl Shutsemau , akpm@linux-foundation.org, david@kernel.org, ljs@kernel.org, hannes@cmpxchg.org, usama.arif@linux.dev Cc: lance.yang@linux.dev, ziy@nvidia.com, hughd@google.com, baolin.wang@linux.alibaba.com, baohua@kernel.org, liam@infradead.org, nico.pache@linux.dev, dev.jain@arm.com, ryan.roberts@arm.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, "Kiryl Shutsemau (Meta)" References: <20260826162101.1314941-1-kirill@shutemov.name> Content-Language: en-US From: Balbir Singh In-Reply-To: <20260826162101.1314941-1-kirill@shutemov.name> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ClientProxiedBy: MEVPR01CA0038.ausprd01.prod.outlook.com (2603:10c6:220:1ff::11) To CH1PR12MB9670.namprd12.prod.outlook.com (2603:10b6:610:2af::6) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CY1PR12MB9651:EE_|IA0PR12MB8694:EE_ 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WaIkBy99GkRLmt3ffZzOVj4JgGDAQpsItMwXwa+QvMDUjMVMcUwEzJE24RN/IuFDknoK28HtTDQJvCJle7xwubEpIt+7FvGAcdW7wtMEZasnGGOlkRotDrrGoFu24taMjzzV/7b2z4lQIecmMkOz0BO2aZT/1w4GoPB6Jqlrb/e+5Tb/9xaMnApIru5gDLdMwuDw+Be1BmQzcIUAKGYU/MxNr8liRaugERxGOHRQz2r4yAbMVGpzjn6dJ+SN7xgfhd0psiV6GtigN5I3Q/cU2JUCL3EKU12bH3Ovqfh5CQNbDESTzi+WuontSuLotuMlPCZrsmFzxXhAn0slIUX0pVKKSWO80cFINkCdztQBm4vG7wx8THuGFGwZi7dpBRpmWWEmXrC1knlOQpHPNJviy+M143M6zZPMGcS8HQLZkB9MT1z6eNmmzjWsRwHZt8qbE/QVfqipWgnkpOF+1H6qarG+YLTdCVJV1DmjTX9EZ8CHKFfc= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 8/27/26 2:20 AM, Kiryl Shutsemau wrote: > From: "Kiryl Shutsemau (Meta)" > > deferred_split_isolate() probes each queued folio with folio_try_get(). > folio_try_get() failure is treated as a lost race with folio_put(). > > It leads to wrong results when !folio_try_get() was not caused by > folio_put(): for a frozen folio, PG_partially_mapped gets wrongfully > cleared and the folio dropped from the queue. > > It came up in the review of my collapse RFC series: > > https://lore.kernel.org/all/20260824131224.73344-1-lance.yang@linux.dev/ > > The bug is inert in upstream code: > > - __folio_split() works around it; > - __folio_migrate_mapping() freezes a folio it is about to replace; > - reclaim freezes only what try_to_unmap() already unmapped. > > No stable@ needed. But my collapse rework steps on it, so it is worth > fixing. > > The first patch fixes deferred_split_isolate(). > > The second patch removes the workaround for this deferred_split_isolate() > behaviour from __folio_freeze_and_split_unmapped(). > > The other three patches are trivial cleanups in > __folio_freeze_and_split_unmapped() that I stumbled on while looking at > it. > > Tested in a VM: split_huge_page_test, folio_split_race_test and cow pass. > > Also ran a test that leaves 16 partially mapped THPs on the deferred split > queue and drives thp-deferred_split through debugfs, checking > nr_anon_partially_mapped. > > Kiryl Shutsemau (Meta) (5): > mm/huge_memory: do not touch frozen folios in deferred_split_isolate() > mm/huge_memory: dequeue the deferred split after the split freeze > mm/huge_memory: reduce indent level in > __folio_freeze_and_split_unmapped() > mm/huge_memory: fold nested ifs in __folio_freeze_and_split_unmapped() > mm/huge_memory: turn the swapcache-with-mapping error case into an > assert > > mm/huge_memory.c | 260 ++++++++++++++++++++--------------------------- > 1 file changed, 109 insertions(+), 151 deletions(-) > > > base-commit: 33f61b12d297562321533c048e034b1fb21c1cf3 Thanks, any chance you ran hmm-tests on these? If not, I can run them and provide some testing coverage from a zone device folio perspective Balbir