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Wong" , Christoph Hellwig , John Hubbard , david@fromorbit.com, nvdimm@lists.linux.dev, akpm@linux-foundation.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH v3 10/25] fsdax: Introduce pgmap_request_folios() Message-ID: References: <166579181584.2236710.17813547487183983273.stgit@dwillia2-xfh.jf.intel.com> <166579187573.2236710.10151157417629496558.stgit@dwillia2-xfh.jf.intel.com> <877d0z0wsl.fsf@nvidia.com> <634db5c1f602_4da3294c3@dwillia2-xfh.jf.intel.com.notmuch> <634dc046bada2_4da329484@dwillia2-xfh.jf.intel.com.notmuch> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <634dc046bada2_4da329484@dwillia2-xfh.jf.intel.com.notmuch> X-ClientProxiedBy: BL0PR02CA0046.namprd02.prod.outlook.com (2603:10b6:207:3d::23) To LV2PR12MB5869.namprd12.prod.outlook.com (2603:10b6:408:176::16) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: LV2PR12MB5869:EE_|DM6PR12MB5520:EE_ X-MS-Office365-Filtering-Correlation-Id: 673433a1-4191-4869-835d-08dab09b6283 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=Ux2F1gIk; arc=pass ("microsoft.com:s=arcselector9901:i=1"); spf=pass (imf04.hostedemail.com: domain of jgg@nvidia.com designates 40.107.92.41 as permitted sender) smtp.mailfrom=jgg@nvidia.com; dmarc=pass (policy=reject) header.from=nvidia.com X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: E064240029 X-Stat-Signature: a4hggunhfzuncp97xi6aza7pbozb9kr7 X-Rspam-User: X-HE-Tag: 1666051066-702050 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 Mon, Oct 17, 2022 at 01:51:18PM -0700, Dan Williams wrote: > > A good design is that nothing has a struct folio * unless it can also > > prove it has a non-zero refcount on it, and that is simply impossible > > for any caller at this point. > > I agree that's a good design, and I think it is a bug to make this > request on anything but a zero-refcount folio, but plumbing pgmap > offsets to replace pfn_to_page() would require dax_direct_access() to > shift from a pfn lookup to a pgmap + offset lookup. That is fair for this series, but maybe the other pgmap users shouldn't be converted to use this style of API? Jason