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Fri, 19 Nov 2021 19:26:52 +0000 Message-ID: <6925ff6e-2cd5-574c-7802-e436a9a2a938@oracle.com> Date: Fri, 19 Nov 2021 19:26:44 +0000 Subject: Re: [PATCH v5 8/8] device-dax: compound devmap support Content-Language: en-US To: Jason Gunthorpe Cc: Dan Williams , linux-mm@kvack.org, Vishal Verma , Dave Jiang , Naoya Horiguchi , Matthew Wilcox , John Hubbard , Jane Chu , Muchun Song , Mike Kravetz , Andrew Morton , Jonathan Corbet , Christoph Hellwig , nvdimm@lists.linux.dev, linux-doc@vger.kernel.org References: <20211112150824.11028-1-joao.m.martins@oracle.com> <20211112150824.11028-9-joao.m.martins@oracle.com> <20211112153404.GD876299@ziepe.ca> <01f36268-4010-ecea-fee5-c128dd8bb179@oracle.com> <20211115164909.GF876299@ziepe.ca> <4d74bfb8-2cff-237b-321b-05aff34c1e5d@oracle.com> <3b7f9516-a35a-e46e-83d4-3059a959d221@oracle.com> <20211119165530.GJ876299@ziepe.ca> From: Joao Martins In-Reply-To: <20211119165530.GJ876299@ziepe.ca> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ClientProxiedBy: LO4P123CA0391.GBRP123.PROD.OUTLOOK.COM (2603:10a6:600:18f::18) To BLAPR10MB4835.namprd10.prod.outlook.com (2603:10b6:208:331::11) MIME-Version: 1.0 Received: from [10.175.193.46] (138.3.204.46) by LO4P123CA0391.GBRP123.PROD.OUTLOOK.COM (2603:10a6:600:18f::18) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4713.22 via Frontend Transport; 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dkim=pass header.d=oracle.com header.s=corp-2021-07-09 header.b=iydBI+19; dkim=pass header.d=oracle.onmicrosoft.com header.s=selector2-oracle-onmicrosoft-com header.b=FGr9YPGd; spf=none (imf25.hostedemail.com: domain of joao.m.martins@oracle.com has no SPF policy when checking 205.220.177.32) smtp.mailfrom=joao.m.martins@oracle.com; dmarc=pass (policy=none) header.from=oracle.com X-HE-Tag: 1637350022-841511 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 11/19/21 16:55, Jason Gunthorpe wrote: > On Fri, Nov 19, 2021 at 04:12:18PM +0000, Joao Martins wrote: > >>> Dan, any thoughts (see also below) ? You probably hold all that >>> history since its inception on commit 2232c6382a4 ("device-dax: Enable page_mapping()") >>> and commit 35de299547d1 ("device-dax: Set page->index"). >>> >> Below is what I have staged so far as a percursor patch (see below scissors mark). >> >> It also lets me simplify compound page case for __dax_set_mapping() in this patch, >> like below diff. >> >> But I still wonder whether this ordering adjustment of @mapping setting is best placed >> as a percursor patch whenever pgmap/page refcount changes happen. Anyways it's just a >> thought. > > naively I would have thought you'd set the mapping on all pages when > you create the address_space and allocate pages into it. Today in fsdax/device-dax (hugetlb too) this is set on fault and set once only (as you say) on the mapped pages. fsdax WARN_ON() you when you clearing a page mapping that was not set to the expected address_space (similar to what I did here) Similar to what I do in the previous snippet I pasted. Except that maybe I should just clear the mapping rather than clearing if f_mapping is the expected one. > AFAIK devmap > assigns all pages to a single address_space, so shouldn't the mapping > just be done once? Isn't it a bit more efficient that you set only when you try to map a page? I take it that's why it is being done this way. Joao