From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8D080C282D7 for ; Wed, 30 Jan 2019 19:48:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 674872084C for ; Wed, 30 Jan 2019 19:48:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1733135AbfA3Tso (ORCPT ); Wed, 30 Jan 2019 14:48:44 -0500 Received: from ale.deltatee.com ([207.54.116.67]:40874 "EHLO ale.deltatee.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727046AbfA3Tso (ORCPT ); Wed, 30 Jan 2019 14:48:44 -0500 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 1govqd-0008Qp-Gb; Wed, 30 Jan 2019 12:48:36 -0700 To: Jason Gunthorpe Cc: Christoph Hellwig , 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> <20190130191946.GD17080@mellanox.com> From: Logan Gunthorpe Message-ID: <3793c115-2451-1479-29a9-04bed2831e4b@deltatee.com> Date: Wed, 30 Jan 2019 12:48:33 -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: <20190130191946.GD17080@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) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2019-01-30 12:19 p.m., Jason Gunthorpe wrote: > On Wed, Jan 30, 2019 at 11:13:11AM -0700, Logan Gunthorpe wrote: >> >> >> 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 only user change here is that more things will succeed when > creating RDMA MRs (and vice versa to GPU). I don't think this > restricts the kernel implementation at all, unless we intend to > remove P2P entirely.. Well for MRs I'd expect you are using struct pages to track the memory some how.... VMAs that aren't backed by pages and use this special interface must therefore be creating new special interfaces that can call p2p_[un]map... I'd much rather see special cases around struct page so we can find ways to generalize it in the future than create special cases tied to random userspace interfaces. Logan