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[207.54.116.67]) by mx.google.com with ESMTPS id j15si1524099itk.24.2019.01.30.10.13.25 for (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Wed, 30 Jan 2019 10:13:26 -0800 (PST) Received-SPF: pass (google.com: domain of logang@deltatee.com designates 207.54.116.67 as permitted sender) client-ip=207.54.116.67; Authentication-Results: mx.google.com; spf=pass (google.com: domain of logang@deltatee.com designates 207.54.116.67 as permitted sender) smtp.mailfrom=logang@deltatee.com Received: from s01061831bf6ec98c.cg.shawcable.net ([68.147.80.180] helo=[192.168.6.205]) by ale.deltatee.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.89) (envelope-from ) id 1gouMO-0007KC-FJ; Wed, 30 Jan 2019 11:13:17 -0700 To: Jason Gunthorpe , Christoph Hellwig Cc: Jerome Glisse , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , Greg Kroah-Hartman , "Rafael J . Wysocki" , Bjorn Helgaas , Christian Koenig , Felix Kuehling , "linux-pci@vger.kernel.org" , "dri-devel@lists.freedesktop.org" , Marek Szyprowski , Robin Murphy , Joerg Roedel , "iommu@lists.linux-foundation.org" References: <20190129174728.6430-1-jglisse@redhat.com> <20190129174728.6430-4-jglisse@redhat.com> <20190129191120.GE3176@redhat.com> <20190129193250.GK10108@mellanox.com> <99c228c6-ef96-7594-cb43-78931966c75d@deltatee.com> <20190129205827.GM10108@mellanox.com> <20190130080208.GC29665@lst.de> <20190130174424.GA17080@mellanox.com> From: Logan Gunthorpe Message-ID: Date: Wed, 30 Jan 2019 11:13:11 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: <20190130174424.GA17080@mellanox.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-SA-Exim-Connect-IP: 68.147.80.180 X-SA-Exim-Rcpt-To: iommu@lists.linux-foundation.org, jroedel@suse.de, robin.murphy@arm.com, m.szyprowski@samsung.com, dri-devel@lists.freedesktop.org, linux-pci@vger.kernel.org, Felix.Kuehling@amd.com, christian.koenig@amd.com, bhelgaas@google.com, rafael@kernel.org, gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, jglisse@redhat.com, hch@lst.de, jgg@mellanox.com X-SA-Exim-Mail-From: logang@deltatee.com Subject: Re: [RFC PATCH 3/5] mm/vma: add support for peer to peer to device vma X-SA-Exim-Version: 4.2.1 (built Tue, 02 Aug 2016 21:08:31 +0000) X-SA-Exim-Scanned: Yes (on ale.deltatee.com) 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 2019-01-30 10:44 a.m., Jason Gunthorpe wrote: > I don't see why a special case with a VMA is really that different. Well one *really* big difference is the VMA changes necessarily expose specialized new functionality to userspace which has to be supported forever and may be difficult to change. The p2pdma code is largely in-kernel and we can rework and change the interfaces all we want as we improve our struct page infrastructure. I'd also argue that p2pdma isn't nearly as specialized as this VMA thing and can be used pretty generically to do other things. Though, the other ideas we've talked about doing are pretty far off and may have other challenges. Logan