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[216.228.121.64]) by mx.google.com with ESMTPS id 207si17322350ywq.155.2019.07.25.11.19.09 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 25 Jul 2019 11:19:10 -0700 (PDT) Received-SPF: pass (google.com: domain of rcampbell@nvidia.com designates 216.228.121.64 as permitted sender) client-ip=216.228.121.64; Authentication-Results: mx.google.com; dkim=pass header.i=@nvidia.com header.s=n1 header.b=OrB98rUK; spf=pass (google.com: domain of rcampbell@nvidia.com designates 216.228.121.64 as permitted sender) smtp.mailfrom=rcampbell@nvidia.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=nvidia.com Received: from hqpgpgate102.nvidia.com (Not Verified[216.228.121.13]) by hqemgate15.nvidia.com (using TLS: TLSv1.2, DES-CBC3-SHA) id ; Thu, 25 Jul 2019 11:19:17 -0700 Received: from hqmail.nvidia.com ([172.20.161.6]) by hqpgpgate102.nvidia.com (PGP Universal service); Thu, 25 Jul 2019 11:19:09 -0700 X-PGP-Universal: processed; by hqpgpgate102.nvidia.com on Thu, 25 Jul 2019 11:19:09 -0700 Received: from rcampbell-dev.nvidia.com (10.124.1.5) by HQMAIL107.nvidia.com (172.20.187.13) with Microsoft SMTP Server (TLS) id 15.0.1473.3; Thu, 25 Jul 2019 18:19:08 +0000 Subject: Re: [PATCH v3 1/3] mm: document zone device struct page field usage To: Christoph Hellwig CC: , , John Hubbard , Matthew Wilcox , Vlastimil Babka , Christoph Lameter , Dave Hansen , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , "Kirill A . Shutemov" , Lai Jiangshan , Martin Schwidefsky , Pekka Enberg , Randy Dunlap , Andrey Ryabinin , Jason Gunthorpe , Andrew Morton , Linus Torvalds References: <20190724232700.23327-1-rcampbell@nvidia.com> <20190724232700.23327-2-rcampbell@nvidia.com> <20190725053821.GA24527@lst.de> X-Nvconfidentiality: public From: Ralph Campbell Message-ID: <8acce6b0-7e84-9dc6-9268-eaf0e814d994@nvidia.com> Date: Thu, 25 Jul 2019 11:19:07 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: <20190725053821.GA24527@lst.de> X-Originating-IP: [10.124.1.5] X-ClientProxiedBy: HQMAIL101.nvidia.com (172.20.187.10) To HQMAIL107.nvidia.com (172.20.187.13) Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nvidia.com; s=n1; t=1564078757; bh=Qao2t1CrfNdMKoMvCh94dTKdtpC+EI45d5wLIIGgET0=; h=X-PGP-Universal:Subject:To:CC:References:X-Nvconfidentiality:From: Message-ID:Date:User-Agent:MIME-Version:In-Reply-To: X-Originating-IP:X-ClientProxiedBy:Content-Type:Content-Language: Content-Transfer-Encoding; b=OrB98rUKTadk/d8iIGA0ZOIqqnVmAn2Gd/fFnuSL26pd/r5Tax28SSiAFMrnrbU+D SInaELtAsdLvh1iYAAkif/sblYyfYzv3b9qGdoSGaZtsLotIAi/jJoglZpjOHgjsi1 Yn51vJ4bQCcYhCTwfcnYmvTNgvpkQOXXM8nWn+wuYBisyfzkxHWVL+79VJum4Mj5Pf w3GDnLSrvzxCgFScHswqu3fju9uqDWp9eZW4sqcsystYZL0gCfffYhsaaDPtEdGcCJ kWJq0QuG2fd9qi5LuW+Pa2TavLm2wnyDUWnB4mFBBnEFSdaKiSwy51ELb249H9GSRf +KQD6RUNBkkoQ== 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 7/24/19 10:38 PM, Christoph Hellwig wrote: > On Wed, Jul 24, 2019 at 04:26:58PM -0700, Ralph Campbell wrote: >> Struct page for ZONE_DEVICE private pages uses the page->mapping and >> and page->index fields while the source anonymous pages are migrated to >> device private memory. This is so rmap_walk() can find the page when >> migrating the ZONE_DEVICE private page back to system memory. >> ZONE_DEVICE pmem backed fsdax pages also use the page->mapping and >> page->index fields when files are mapped into a process address space. >> >> Add comments to struct page and remove the unused "_zd_pad_1" field >> to make this more clear. > > I still think we should also fix up the layout, and I haven't seen > a reply from Matthew justifying his curses for your patch that makes > the struct page layout actually match how it is used. > Well, I can kind of see this both ways since ZONE_DEVICE MEMORY_DEVICE_DEVDAX and MEMORY_DEVICE_PCI_P2PDMA don't seem to use the 3 words like MEMORY_DEVICE_PRIVATE and MEMORY_DEVICE_FS_DAX. I like v3 because not all of the ZONE_DEVICE types are handled the same in regards to using the 3 words and there may be future ZONE_DEVICE types that use the 3 words differently which might require a union. I agree, I would like to hear from Matthew on his thoughts.