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Shutemov" , Pavel Begunkov , Mika Penttila , David Howells , Christoph Hellwig References: <6b73e692c2929dc4613af711bdf92e2ec1956a66.1682638385.git.lstoakes@gmail.com> <094d2074-5b69-5d61-07f7-9f962014fa68@redhat.com> <400da248-a14e-46a4-420a-a3e075291085@redhat.com> <077c4b21-8806-455f-be98-d7052a584259@lucifer.local> <62ec50da-5f73-559c-c4b3-bde4eb215e08@redhat.com> From: John Hubbard In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ClientProxiedBy: SJ0PR05CA0052.namprd05.prod.outlook.com (2603:10b6:a03:33f::27) To BY5PR12MB4130.namprd12.prod.outlook.com (2603:10b6:a03:20b::16) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BY5PR12MB4130:EE_|CH3PR12MB8660:EE_ X-MS-Office365-Filtering-Correlation-Id: f2052b31-d3c7-473d-a530-08db48160698 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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dcrX8GRBOJ17l5XaiXeA+I1cNs+vX81fAtmeTqnWUYnPVlID5t+Vz6vfm9av6fw5IqZzJeyuSrjR/JyTZWayDgcKJeTPWW1mQKRW8fJg2qpVtRtXFtH7Ri+ZVOmYJASuN/0nf0446WPuHNo+AKOuxcKXGRSeTHwTYLBlNwPpGwl5LCG25Y54uqhumScz8gS9kUgLxTpn+KHyPrx8Y2JpguVuJivL97AyLVd6uw+5KjX2UpgDJkLWuVgQtqDoqHzq20leKFKb+aWAJAVy11pWIqvs5bqVC/qR/H3N8 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: On 4/28/23 10:33, Jason Gunthorpe wrote: > On Fri, Apr 28, 2023 at 11:56:55AM -0400, Peter Xu wrote: > >>> PageAnon(page) can be called from GUP-fast after grabbing a reference. See >>> gup_must_unshare(). >> >> Hmm.. Is it a good idea at all to sacrifise all "!anon" fast-gups for this? >> People will silently got degrade even on legal pins on shmem/hugetlb, I >> think, which seems to be still a very major use case. > > Remember gup fast was like this until quite recently - DAX wrecked it. > > I fixed it when I changed DAX to not post-scan the VMA list.. > > I'm not sure longterm and really fast need to go together. > Exactly: gup_fast + FOLL_LONGTERM is asking too much of this system, it's really excessive. I like the idea of simply: "if (FOLL_LONGTERM) jump straight to slow gup". thanks, -- John Hubbard NVIDIA