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Shutemov" , Alex Williamson , Andrea Arcangeli , LKML , linux-mm@kvack.org, Jason Gunthorpe References: <20220203093232.572380-1-jhubbard@nvidia.com> <20220203093232.572380-5-jhubbard@nvidia.com> From: John Hubbard In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: BY5PR16CA0016.namprd16.prod.outlook.com (2603:10b6:a03:1a0::29) To BY5PR12MB4130.namprd12.prod.outlook.com (2603:10b6:a03:20b::16) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 129405b1-5fc4-4561-0f1f-08d9e75bf547 X-MS-TrafficTypeDiagnostic: DM5PR1201MB2488:EE_ X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:6790; 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:BY5PR12MB4130.namprd12.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230001)(4636009)(366004)(5660300002)(6916009)(66556008)(6486002)(4744005)(7416002)(54906003)(66946007)(6512007)(66476007)(508600001)(83380400001)(2616005)(31686004)(2906002)(107886003)(316002)(26005)(186003)(38100700002)(31696002)(86362001)(36756003)(6506007)(8936002)(8676002)(4326008)(53546011)(45980500001)(43740500002);DIR:OUT;SFP:1101; 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The purpose of >> get_user_pages_locked() is to allow for unlocking the mmap_lock when >> reading a page from the disk during a page fault (hidden behind >> VM_FAULT_RETRY). The idea is to reduce contention on the heavily-used >> mmap_lock. (Thanks to Jan Kara for clearly pointing that out, and in >> fact I've used some of his wording here.) >> >> However, it is unlikely for lookup_node() to take a page fault. With >> that in mind, change over to calling get_user_pages_fast(). This >> simplifies the code, runs a little faster in the expected case, and >> allows removing get_user_pages_locked() entirely. > > Maybe split the lookup_node changes into a separate patch, as that > allows to document that change even better. OK, I'll do that. thanks, -- John Hubbard NVIDIA