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Wong" , John Hubbard , Matthew Wilcox , linux-mm@kvack.org, nvdimm@lists.linux.dev, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH 00/13] Fix the DAX-gup mistake Message-ID: References: <6317a26d3e1ed_166f2946e@dwillia2-xfh.jf.intel.com.notmuch> <6317ebde620ec_166f29466@dwillia2-xfh.jf.intel.com.notmuch> <6318d07fa17e7_166f29495@dwillia2-xfh.jf.intel.com.notmuch> <6318e66861c87_166f294f1@dwillia2-xfh.jf.intel.com.notmuch> <631902ef5591a_166f2941c@dwillia2-xfh.jf.intel.com.notmuch> <631a420ad2f28_166f29423@dwillia2-xfh.jf.intel.com.notmuch> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <631a420ad2f28_166f29423@dwillia2-xfh.jf.intel.com.notmuch> X-ClientProxiedBy: BL0PR1501CA0011.namprd15.prod.outlook.com (2603:10b6:207:17::24) To MN2PR12MB4192.namprd12.prod.outlook.com (2603:10b6:208:1d5::15) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: MN2PR12MB4192:EE_|DS7PR12MB5741:EE_ X-MS-Office365-Filtering-Correlation-Id: 7a108c50-9d16-4e8f-a99c-08da9259eeb5 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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dkim=pass header.d=Nvidia.com header.s=selector2 header.b=tfLIoJnw; dmarc=pass (policy=reject) header.from=nvidia.com; arc=pass ("microsoft.com:s=arcselector9901:i=1"); spf=pass (imf24.hostedemail.com: domain of jgg@nvidia.com designates 40.107.236.40 as permitted sender) smtp.mailfrom=jgg@nvidia.com X-Rspam-User: X-Rspamd-Server: rspam01 X-Stat-Signature: fk73m7g8ksd4q7ts6f5t65tifc51mgdn X-Rspamd-Queue-Id: 5A62D1800A1 X-HE-Tag: 1662724420-717942 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 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. 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. > > I'm not sure what it has to do with normal_page? > > This thread is mainly about DAX slowly reinventing _mapcount that gets > managed in all the right places for a normal_page. Longer term I think > we either need to get back to the page-less DAX experiment and find a > way to unwind some of this page usage creep, or cut over to finally > making DAX-pages be normal pages and delete most of the special case > handling in fs/dax.c. I am open to discussing the former, but I think > the latter is more likely. I think the latter is inevitable at this point.. Jason