From mboxrd@z Thu Jan 1 00:00:00 1970 From: Logan Gunthorpe Subject: Re: [RFC PATCH 3/5] mm/vma: add support for peer to peer to device vma Date: Wed, 30 Jan 2019 11:13:11 -0700 Message-ID: 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> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20190130174424.GA17080@mellanox.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org 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" List-Id: iommu@lists.linux-foundation.org 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