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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?xcBAcB8P+wKBHKVhHHRTH6Wkp2Dx6htbak6eLckjkQXC8O0LDp1BI/mnPMag?= =?us-ascii?Q?Nna9YWTnYmwE8+Gprad0EhO9dSKMqevln4nSnfY1bLai65zGwOhx4caBCxvR?= =?us-ascii?Q?yAkLZGwAbh7QC6VDo2SGwC6XGDmAa8FRqjaNoT52aYKMMPh9JjKVWMr0ZoTX?= =?us-ascii?Q?iFitGnKskdns6DegTP++m3rNFPrxrCBc3RRK274Penc+wPnYhZ2OZUH3KEtV?= =?us-ascii?Q?V+s02f+uOm67J2AqnOAmPSN2/6dhT0pAxKWlC+UWDq5+0Vz8+4sRlVRvbdLW?= =?us-ascii?Q?NgGxO05vqwpDEW9TFTrql+ph8vBP/2zFnW8Yq9CIr5QGHRS3FXU3wleIvQiZ?= =?us-ascii?Q?vkR7WJ6J1AlIVG0IueuqL07Go+B8l/SGETHfXQLe5rMUXA2CY+VkWlB1Um0T?= =?us-ascii?Q?kbLULZsZoAuRtXfQuRwZ8wTJi0TahmtLxvfLcJUnc+mwjtIeXMzlgsroiWHD?= =?us-ascii?Q?XDTDitDZzUFKD98b9fkFLcqs/ytIOkpbpQXOcfagXJcI10xzRli7vsncDT0s?= =?us-ascii?Q?Dg3YeLU4qX21OUFUWIYoxKqJk6q9t0lTseh1H8z4rto+RUCz/rEJjslMOVSM?= =?us-ascii?Q?tx0KfZyTIzUgK42lkUcdpBDirQhnC73np0Mhl9STJZ7nAqkOkYV1xOlfeymZ?= =?us-ascii?Q?EUSWZxDZyYQqku4cZBtjnHKQJLCJ4jibhlA7yeEPk433Ij6AuV5AN7UklRY0?= =?us-ascii?Q?OO6kTxuaqkiCPlvyvk9JGyvIaM12Hmb5b3VZZxv3U2viOyPYfe+5P1Cv2+YK?= =?us-ascii?Q?/jIe4QFbjrSwRSLn8MJ9KbnfML6/3ZLcVzfdfHYuT9PNQMrguJOtm7GsGDhB?= =?us-ascii?Q?+BedvQOsux8LIdI9G3AUMAhrGeUgfHmKNiUoYUhX7UqCfTBciTYzj6tCXhbs?= =?us-ascii?Q?3U0jB+UkOYK8Dp9SY2PJ1eh9wVq2EGL+rYLjuoPSBL89ml3g4CzUiTLqBViG?= =?us-ascii?Q?OqEXjxBW6JAavNcJalyiBzdK0oGY37IPI3dvtin9zWvBELcrFQrTMmndWhA1?= =?us-ascii?Q?pSG8/IC/G7UQl+CtfDJcrQFc4NNIpbFecl82UCIq5rzLa0ITmkCdXEc5emiO?= =?us-ascii?Q?mKiXadQUK8VkeVsLjVFTORqnNrgBPG5ouSsmJ+WAYvHvI7IxL35eG6a3/Evn?= =?us-ascii?Q?/g/pGY4YVmXWeOWWNCZlDivwMH34sNZv9XjDmsfofilrmDDafMAQgh59k5uQ?= =?us-ascii?Q?Dk1t/ihRz9tKL0lNnMTLUQxzcbB4fm2fRpjPZXxIyAQVQY9G1/9Gih5+hZnV?= =?us-ascii?Q?GCnozcL7E/EDOPMlkl49WYYrDy9GGmfzVLyaN5Hneif030aNdCV2seXE1wpe?= =?us-ascii?Q?zn8KFFpYtdabr+BIP83CVk8eTLLrskK136iyj7mS3NVa9w+vLmQZqTzAFb1u?= =?us-ascii?Q?ccqjPQzoa6UUkpumn27rXlQqARCHR2fP9cVDRE0FSsHja9jnHpios//YTtGs?= =?us-ascii?Q?k6Jxj/d42J+6g0dqTioDQrBLl7aI9EUczwhZriqR6uwpZXmrHvM9g+0oXitB?= =?us-ascii?Q?5gnXJS4tIQ2AKr2Z1YBSmC3Nq0rZG/qlTzCfgiAHaBrkxi3aegbXeYeK/lgH?= =?us-ascii?Q?H1vP1cKNmUfPiYVaJKZXLqnwGwKPowgntrCqwK4WKpQRhVxw13QFLpxZNaMo?= =?us-ascii?Q?uA=3D=3D?= X-MS-Exchange-CrossTenant-Network-Message-Id: c54439a6-b2ff-413d-87de-08da928c0b03 X-MS-Exchange-CrossTenant-AuthSource: MWHPR1101MB2126.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 09 Sep 2022 17:52:20.6078 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 46c98d88-e344-4ed4-8496-4ed7712e255d X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: 2Jdg7SmYgH+mzq3abMidtwb0uHH5bHGmhHzxJ2nXh6VG6qNi2+/qcpSrZLgiu84/Xj4ymBxbVsa2oqXQ6mlKP8dAO6+1wYf+FhhH58KtnDE= X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH0PR11MB5625 X-OriginatorOrg: intel.com Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Jason Gunthorpe wrote: > On Thu, Sep 08, 2022 at 12:27:06PM -0700, Dan Williams wrote: > > flag lets the fsdax core track when it has already dropped a page > > reference, but still has use for things like memory-failure to > > opportunistically use page->mapping on a 0-reference page. > > This is not straightforward, as discussed before the page->mapping is > allowed to change while the refcount is zero, so there is no generic > way to safely obtain a pointer to the address space from a 0 reference > page. Agree. > > You'd have to pass the 0 reference page into a new pgmap operation > which could obtain an appropriate internal lock to read page->mapping. Correct, that's what the memory-failure code does via dax_lock_page(). It pins the pgmap, freezes page->mapping associations via rcu_read_lock(), speculatively reads page->mapping, takes the Xarray lock, revalidates page->mapping is the one we read speculatively, and then finally locks the entry in place until the memory-failure handling completes.