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Mar 2024 06:03:29 +0000 Date: Wed, 20 Mar 2024 23:03:27 -0700 From: Dan Williams To: Alistair Popple CC: Dan Williams , , , , , , , , , , , , Subject: Re: ZONE_DEVICE refcounting Message-ID: <65fbcdaf2042f_aa222948c@dwillia2-mobl3.amr.corp.intel.com.notmuch> References: <87ttlhmj9p.fsf@nvdebian.thelocal> <65f148866bc56_a9b42947@dwillia2-mobl3.amr.corp.intel.com.notmuch> <87y1ad776c.fsf@nvdebian.thelocal> <878r2c6t99.fsf@nvdebian.thelocal> Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <878r2c6t99.fsf@nvdebian.thelocal> X-ClientProxiedBy: MW4P222CA0021.NAMP222.PROD.OUTLOOK.COM (2603:10b6:303:114::26) To PH8PR11MB8107.namprd11.prod.outlook.com (2603:10b6:510:256::6) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: PH8PR11MB8107:EE_|IA0PR11MB8397:EE_ X-MS-Office365-Filtering-Correlation-Id: 9e73de79-96ed-414c-16f9-08dc496ca1ac X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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 WRlA+E+0 ZVcy5HXaBH4Dtt740yvpyMBt1Hb/U5JKXD598sjK4w7YBrXHPo5A9UCLlsBLxe9UW+Kra7YM9L8W5KWDD7kOSmtXRTOJukfMsms5QNyzsx9YEnY+6Rz9QKnaAibUC+zh0RUYG05diFoXT9zcJDn2DVnzNVw39f0Pf9NJjcqI8x/X7dpu1p7ECT0LV5E8ygB5l2E+nP22FBCsnvaG/pmvREihkS5QSn3lSpeB2spuo+j5u9ob5TR8iPc4sUdyR7X8ocRU08TiD/DCDsQzKWILcCNocXoXCYVScvDsE33P80vF5R2j8alKA0dILg3HRt6uaeqLKAA1QSB+o3wqyImP9j8IP7DDuM+OQekUuyAghMzhWKCc= 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: List-Subscribe: List-Unsubscribe: Alistair Popple wrote: > > Alistair Popple writes: > > > Dan Williams writes: > > > >> Alistair Popple wrote: > > > > I also noticed folio_anon() is not safe to call on a FS DAX page due to > > sharing PAGE_MAPPING_DAX_SHARED. > > Also it feels like I could be missing something here. AFAICT the > page->mapping and page->index fields can't actually be used outside of > fs/dax because they are overloaded for the shared case. Therefore > setting/clearing them could be skipped and the only reason for doing so > is so dax_associate_entry()/dax_disassociate_entry() can generate > warnings which should never occur anyway. So all that code is > functionally unnecessary. What do you mean outside of fs/dax, do you literally mean outside of fs/dax.c, or the devdax case (i.e. dax without fs-entanglements)? Memory failure needs ->mapping and ->index to rmap dax pages. See mm/memory-failure.c::__add_to_kill() and mm/memory-failure.c::__add_to_kill_fsdax() where that latter one is for cases where the fs needs has signed up to react to dax page failure.