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Tue, 23 Feb 2021 17:18:29 +0000 Subject: Re: [PATCH RFC 1/9] memremap: add ZONE_DEVICE support for compound pages To: Dan Williams Cc: Linux MM , Ira Weiny , linux-nvdimm , Matthew Wilcox , Jason Gunthorpe , Jane Chu , Muchun Song , Mike Kravetz , Andrew Morton , John Hubbard References: <20201208172901.17384-1-joao.m.martins@oracle.com> <20201208172901.17384-2-joao.m.martins@oracle.com> <7249cfd2-c178-2e6a-6b03-307a05f11785@nvidia.com> <7e8908ca-4d0f-6549-0442-d4b15fbc90ab@oracle.com> <94075df6-ab3b-c6e4-13f1-26dd266dbf82@oracle.com> From: Joao Martins Message-ID: Date: Tue, 23 Feb 2021 17:18:20 +0000 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [94.61.1.144] X-ClientProxiedBy: LO4P123CA0312.GBRP123.PROD.OUTLOOK.COM (2603:10a6:600:197::11) To BYAPR10MB3077.namprd10.prod.outlook.com (2603:10b6:a03:8c::12) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [192.168.1.67] (94.61.1.144) by LO4P123CA0312.GBRP123.PROD.OUTLOOK.COM (2603:10a6:600:197::11) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3868.30 via Frontend Transport; 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identity=mailfrom; envelope-from=""; helo=userp2120.oracle.com; client-ip=156.151.31.85 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1614100716-173915 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 2/23/21 4:50 PM, Dan Williams wrote: > On Tue, Feb 23, 2021 at 7:46 AM Joao Martins wrote: >> On 2/22/21 8:37 PM, Dan Williams wrote: >>> On Mon, Feb 22, 2021 at 3:24 AM Joao Martins wrote: >>>> On 2/20/21 1:43 AM, Dan Williams wrote: >>>>> On Tue, Dec 8, 2020 at 9:59 PM John Hubbard wrote: >>>>>> On 12/8/20 9:28 AM, Joao Martins wrote: [...] >>> Don't get me wrong the >>> capability is still needed for filesystem-dax, but the distinction is >>> that vmemmap_populate_compound_pages() need never worry about an >>> altmap. >>> >> IMO there's not much added complexity strictly speaking about altmap. We still use the >> same vmemmap_{pmd,pte,pgd}_populate helpers which just pass an altmap. So whatever it is >> being maintained for fsdax or other altmap consumers (e.g. we seem to be working towards >> hotplug making use of it) we are using it in the exact same way. >> >> The complexity of the future vmemmap_populate_compound_pages() has more to do with reusing >> vmemmap blocks allocated in previous vmemmap pages, and preserving that across section >> onlining (for 1G pages). > > True, I'm less worried about the complexity as much as > opportunistically converting configurations to RAM backed pages. It's > already the case that poison handling is page mapping size aligned for > device-dax, and filesystem-dax needs to stick with non-compound-pages > for the foreseeable future. > Hmm, I was sort off wondering that fsdax could move to compound pages too as opposed to base pages, albeit not necessarily using the vmemmap page reuse as it splits pages IIUC. > Ok, let's try to keep altmap in vmemmap_populate_compound_pages() and > see how it looks. > OK, will do.