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From:   Jason Gunthorpe <jgg@mellanox.com>
To:     Logan Gunthorpe <logang@deltatee.com>
CC:     Christoph Hellwig <hch@lst.de>, Jerome Glisse <jglisse@redhat.com>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J . Wysocki" <rafael@kernel.org>,
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        Christian Koenig <christian.koenig@amd.com>,
        Felix Kuehling <Felix.Kuehling@amd.com>,
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        Joerg Roedel <jroedel@suse.de>,
        "iommu@lists.linux-foundation.org" <iommu@lists.linux-foundation.org>
Subject: Re: [RFC PATCH 3/5] mm/vma: add support for peer to peer to device
 vma
Thread-Topic: [RFC PATCH 3/5] mm/vma: add support for peer to peer to device
 vma
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Date:   Wed, 30 Jan 2019 19:19:52 +0000
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On Wed, Jan 30, 2019 at 11:13:11AM -0700, Logan Gunthorpe wrote:
>=20
>=20
> 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.
>=20
> 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.=20

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..

Jason