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Tue, 16 Aug 2022 00:53:55 +0000 Received: from BYAPR12MB3176.namprd12.prod.outlook.com ([fe80::eca6:a4a7:e2b2:27e7]) by BYAPR12MB3176.namprd12.prod.outlook.com ([fe80::eca6:a4a7:e2b2:27e7%5]) with mapi id 15.20.5504.027; Tue, 16 Aug 2022 00:53:55 +0000 References: User-agent: mu4e 1.6.9; emacs 27.1 From: Alistair Popple To: Peter Xu Cc: linux-mm@kvack.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, "Sierra Guiza, Alejandro (Alex)" , Felix Kuehling , Jason Gunthorpe , John Hubbard , David Hildenbrand , Ralph Campbell , Matthew Wilcox , Karol Herbst , Lyude Paul , Ben Skeggs , Logan Gunthorpe , linuxram@us.ibm.com, paulus@ozlabs.org Subject: Re: [PATCH 1/2] mm/migrate_device.c: Copy pte dirty bit to page Date: Tue, 16 Aug 2022 10:51:57 +1000 In-reply-to: Message-ID: <87zgg5uhy7.fsf@nvdebian.thelocal> Content-Type: text/plain X-ClientProxiedBy: BYAPR04CA0022.namprd04.prod.outlook.com (2603:10b6:a03:40::35) To BYAPR12MB3176.namprd12.prod.outlook.com (2603:10b6:a03:134::26) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 8b28c564-d6b5-4a02-771b-08da7f21cb8b X-MS-TrafficTypeDiagnostic: DM4PR12MB6349:EE_ X-LD-Processed: 43083d15-7273-40c1-b7db-39efd9ccc17a,ExtAddr X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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b=JcuILEwWNa0RbLrWkMb2RLzgv3jeaRK6niM7OV3q6zoTD0Or4da8afzYWjbKKftrIhjXz5 VIZpmNxgY1comE7+IcC97FMs0gXbuEEvLG68KhdY1wfZInrqbvpFsDv9zUoXEjuNzA5/rK PS5Lc8Gp0fYKnAw1zQlLoQcpZM0ON6o= X-Stat-Signature: rketq74ngch9xs8akzo57kupgkmsjntu X-Rspamd-Queue-Id: 7D9E58002F Authentication-Results: imf02.hostedemail.com; dkim=pass header.d=Nvidia.com header.s=selector2 header.b="t/mJm0Ys"; dmarc=pass (policy=reject) header.from=nvidia.com; arc=pass ("microsoft.com:s=arcselector9901:i=1"); spf=pass (imf02.hostedemail.com: domain of apopple@nvidia.com designates 40.107.102.50 as permitted sender) smtp.mailfrom=apopple@nvidia.com X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1660611237-417968 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Peter Xu writes: > Hi, Alistair, > > On Fri, Aug 12, 2022 at 03:22:30PM +1000, Alistair Popple wrote: >> migrate_vma_setup() has a fast path in migrate_vma_collect_pmd() that >> installs migration entries directly if it can lock the migrating page. >> When removing a dirty pte the dirty bit is supposed to be carried over >> to the underlying page to prevent it being lost. >> >> Currently migrate_vma_*() can only be used for private anonymous >> mappings. That means loss of the dirty bit usually doesn't result in >> data loss because these pages are typically not file-backed. However >> pages may be backed by swap storage which can result in data loss if an >> attempt is made to migrate a dirty page that doesn't yet have the >> PageDirty flag set. >> >> In this case migration will fail due to unexpected references but the >> dirty pte bit will be lost. If the page is subsequently reclaimed data >> won't be written back to swap storage as it is considered uptodate, >> resulting in data loss if the page is subsequently accessed. >> >> Prevent this by copying the dirty bit to the page when removing the pte >> to match what try_to_migrate_one() does. >> >> Signed-off-by: Alistair Popple >> Reported-by: Peter Xu > > This line should be: > > Reported-by: Huang Ying > > Please also feel free to add: > > Acked-by: Peter Xu Thanks Peter, my bad. I assume Andrew can fix up the tags if I don't need to re-spin this series. > Thanks,