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received-spf: None (protection.outlook.com: mellanox.com does not designate permitted sender hosts) x-ms-exchange-senderadcheck: 1 x-microsoft-antispam: BCL:0; x-microsoft-antispam-message-info: /O/CO1YR/uqGacxfPNB5PjqvcSipYG4RfKucbTSoqzBUEs2JZGwMoLL5H2ErOfaAWTECmTb16KUJcs110D2glxRsT4NgYAD8OXzE6VoDBLrh2FgHyZE/s2n09ecnSqaYU736gAjkdZ6lnw7dX318X3kdhzkEUhatzoNs6ASsjKL/Yp48h6S73ZgIYlfzyU5eEQBdLTuPTKRiPC6ZVevzUChbhs9X5NVuZqoVHZnmjjtEcAWUOOgoEHlEbMaQVAem3YAPncn3obHmtjA4A8krGnToMhol8G9UdYwdmX+KmhseMMUoD9QQnWhgVKcGjMojC1Uo7qDzXaGqoSo5DjgId9B6G9iAyG0Y1OnM2LwwRyVxZrfbb48qxfFxPAi5IvZ8goN48UMOSzBu+Q6bSu4fDOOf21XK0j9YzDXKrpi11LreMFSTuMoiuPgaUJ3mjN6L x-ms-exchange-transport-forked: True Content-Type: text/plain; charset="us-ascii" Content-ID: Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: Mellanox.com X-MS-Exchange-CrossTenant-Network-Message-Id: 7dc745f0-4bb3-4783-0814-08d75717076d X-MS-Exchange-CrossTenant-originalarrivaltime: 22 Oct 2019 17:41:11.8543 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: a652971c-7d2e-4d9b-a6a4-d149256f461b X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: sCgnVa8WMZjJUTVgr/YYva50C6fnTVNzeNwLhcWv7vHV8Y3O5g6AvdKgjzEHAIGtQOotGCOjgAy8yojhaTpHjQ== X-MS-Exchange-Transport-CrossTenantHeadersStamped: VI1PR05MB6223 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 Tue, Oct 22, 2019 at 01:30:26PM -0400, Jerome Glisse wrote: > > Smart drivers can test somehow for pfn =3D=3D zero_page and optimize? >=20 > There is nothing to optimize here, i do not know any hardware that > have a special page table entry that make all memory access return > zero. Presumably any GPU could globally dedicate one page of internal memory as a zero page and remap CPU zero page to that internal memory page? This is basically how the CPU zero page works. I suspect mlx5 could do the same with its internal memory, but the internal memory is too limited to make this worth while. mlx5 also has a specially 'zero MR' that always reads as zero (and discards writes), but it doesn't quite fit well into the ODP flow. Jason