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Wong" , Trond Myklebust , Anna Schumaker , Jan Kara , David Hildenbrand , Logan Gunthorpe , linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org, linux-nfs@vger.kernel.org, linux-mm@kvack.org, LKML References: <20220831041843.973026-1-jhubbard@nvidia.com> <20220831041843.973026-5-jhubbard@nvidia.com> <103fe662-3dc8-35cb-1a68-dda8af95c518@nvidia.com> From: John Hubbard In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ClientProxiedBy: BY5PR20CA0007.namprd20.prod.outlook.com (2603:10b6:a03:1f4::20) To DM6PR12MB4140.namprd12.prod.outlook.com (2603:10b6:5:221::13) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 854f191e-6af1-4505-9918-08da8fddad86 X-MS-TrafficTypeDiagnostic: SJ0PR12MB5609:EE_ X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:DM6PR12MB4140.namprd12.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230016)(4636009)(376002)(346002)(366004)(39860400002)(396003)(136003)(7416002)(8936002)(4326008)(8676002)(5660300002)(66556008)(66946007)(6486002)(6506007)(26005)(6512007)(38100700002)(478600001)(6666004)(66476007)(41300700001)(316002)(186003)(6916009)(2616005)(53546011)(54906003)(83380400001)(31686004)(86362001)(31696002)(2906002)(36756003)(45980500001)(43740500002);DIR:OUT;SFP:1101; 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Overall, what >> happens to bvec pages? Leave the get_page() pin in place for FOLL_GET >> (or USE_FOLL_GET), I suppose, but do...what, for FOLL_PIN callers? > > Do not change anyhing for FOLL_GET callers, as they are on the way out > anyway. > OK, got it. > For FOLL_PIN callers, never pin bvec and kvec pages: For file systems > not acquiring a reference is obviously safe, and the other callers will > need an audit, but I can't think of why it woul ever be unsafe. In order to do that, one would need to be confident that such bvec and kvec pages do not get passed down to bio_release_pages() (or the new bio_unpin_pages()). Also, I'm missing a key point, because today bvec pages get a get_page() reference from __iov_iter_get_pages_alloc(). If I just skip that, then the get/put calls are unbalanced... I can just hear Al Viro repeating his points about splice() and vmsplice(), heh. :) thanks, -- John Hubbard NVIDIA