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Howlett" , "Nico Pache" , "Ryan Roberts" , "Dev Jain" , "Lance Yang" , "Usama Arif" , "Kiryl Shutsemau" , "Lorenzo Stoakes" , "Rik van Riel" , "Vlastimil Babka" , "Harry Yoo" , "Jann Horn" , "Johannes Weiner" , "Yosry Ahmed" , "Chengming Zhou" , "Catalin Marinas" , "Will Deacon" , "Mark Rutland" From: "Zi Yan" Subject: Re: [PATCH 2/8] mm/huge_memory: use folio_swap_entry() when splitting a swapcache folio X-Mailer: aerc 0.22.0 References: <20260830-folio_swap_entry-v1-0-7786b52acbc8@columbia.edu> <20260830-folio_swap_entry-v1-2-7786b52acbc8@columbia.edu> In-Reply-To: <20260830-folio_swap_entry-v1-2-7786b52acbc8@columbia.edu> X-ClientProxiedBy: YQBPR0101CA0258.CANPRD01.PROD.OUTLOOK.COM (2603:10b6:c01:68::35) 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_|DS2PR12MB9637:EE_ X-MS-Office365-Filtering-Correlation-Id: ed904f6f-207f-4718-4a01-08df076f2aa4 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|376014|7416014|1800799024|23010399003|56012099006|11063799006|4143699003|10067099003|921020|22082099003|18002099003; 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Use folio_swap_entry() instead. > > No functional change. > > Signed-off-by: Tal Zussman > --- > mm/huge_memory.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 54494c3fa983..03287f995d92 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -3760,7 +3760,7 @@ static void __split_folio_to_order(struct folio *fo= lio, int old_order, > VM_WARN_ON_ONCE_PAGE(new_folio->private, new_head); > =20 > if (folio_test_swapcache(folio)) > - new_folio->swap.val =3D folio->swap.val + i; > + new_folio->swap =3D folio_swap_entry(folio, i); folio_swap_entry() checks folio_nr_pages(folio) internally. folio->_nr_pages is in first tail page of folio. If new_order is 0, it is basically checking memcg_data in the first new_folio. And after first iteration, folio->_nr_page will be clobbered. Without NR_PAGES_IN_LARGE_FOLIO, folio_nr_pages() is derived from folio_order(), which is in folio->_flags_1. It can have the same issue. Please keep it open coded. You can add a comment like "during split, not all folio fields are avaialbe, open code the swap calculation". > =20 > /* Page flags must be visible before we make the page non-compound. */ > smp_wmb(); --=20 Best Regards, Yan, Zi