From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jason Gunthorpe Subject: Re: [RFC PATCH 3/5] mm/vma: add support for peer to peer to device vma Date: Tue, 29 Jan 2019 20:58:35 +0000 Message-ID: <20190129205827.GM10108@mellanox.com> 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> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <99c228c6-ef96-7594-cb43-78931966c75d@deltatee.com> Content-Language: en-US Content-ID: Sender: linux-kernel-owner@vger.kernel.org To: Logan Gunthorpe 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" , Christoph Hellwig , Marek Szyprowski , Robin Murphy , Joerg Roedel , "iommu@lists.linux-foundation.org" List-Id: iommu@lists.linux-foundation.org On Tue, Jan 29, 2019 at 01:39:49PM -0700, Logan Gunthorpe wrote: > implement the mapping. And I don't think we should have 'special' vma's > for this (though we may need something to ensure we don't get mapping > requests mixed with different types of pages...). I think Jerome explained the point here is to have a 'special vma' rather than a 'special struct page' as, really, we don't need a struct page at all to make this work. If I recall your earlier attempts at adding struct page for BAR memory, it ran aground on issues related to O_DIRECT/sgls, etc, etc. This does seem to avoid that pitfall entirely as we can never accidently get into the SGL system with this kind of memory or VMA? Jason