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Howlett" , "Nico Pache" , "Ryan Roberts" , "Dev Jain" , "Barry Song" , "Lance Yang" , "Usama Arif" , "Vlastimil Babka" , "Jann Horn" To: "Kiryl Shutsemau" , "Andrew Morton" , "David Hildenbrand" , "Lorenzo Stoakes" , "Baolin Wang" From: "Zi Yan" X-Mailer: aerc 0.22.0 References: <20260910120238.2529819-1-kirill@shutemov.name> <20260910120238.2529819-10-kirill@shutemov.name> In-Reply-To: <20260910120238.2529819-10-kirill@shutemov.name> X-ClientProxiedBy: YQBPR0101CA0201.CANPRD01.PROD.OUTLOOK.COM (2603:10b6:c01:67::7) 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_|PH7PR12MB6934:EE_ X-MS-Office365-Filtering-Correlation-Id: e5073c25-1685-4186-2b76-08df10150b9a X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|23010399003|7416014|376014|366016|22082099003|18002099003|10067099003|56012099006|11063799006|4143699003|6133799003; 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The scan is called with mmap_lock held for reading and returns > with it still held. The collapse is called without it. > > collapse_single_pmd() kept that boundary inside itself. It dropped the > lock on some paths and not others, and reported which by way of a bool it= s > callers had to carry along and then act on. > > Open-code it in the two callers. Each scans under the lock it already > holds and, on SCAN_SUCCEED, gives the lock up before running the collapse= . > khugepaged's lock_dropped and madvise_collapse()'s mmap_unlocked both go: > the code dropping the lock is now the code that wanted to know. > > khugepaged's walk carries on to the next table while the scan keeps > refusing, and ends once a collapse has taken the lock from under it. > madvise_collapse() re-finds its VMA after a collapse, which it did before= , > and now uses a NULL vma to say that it has to. It still reports the drop > to its own caller, from the line that does it. > > The lock is given up and taken again at the same points as before. No > functional change. > > Assisted-by: LLM > Signed-off-by: Kiryl Shutsemau (Meta) > --- > mm/khugepaged.c | 102 +++++++++++++++++++++++------------------------- > 1 file changed, 49 insertions(+), 53 deletions(-) > LGTM. Thanks. Reviewed-by: Zi Yan One question: What prevents us from doing: while () { 1. mmap_lock 2. scan_pmd 3. mmap_unlock, bail out if needed 4. run_pmd } for both cases? It improves readability. What is the downside of dropping the lock during multiple scans? for madvise_collapse(), I see mmap_read_lock is held when it is called, so it can be dropped at the entry and the code makes sure it is held at the exit. --=20 Best Regards, Yan, Zi