linux-kernel - Re: [RFC PATCH 3/5] mm/vma: add support for peer to peer to device vma

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Message-ID: <20190130191946.GD17080@mellanox.com>
Date:   Wed, 30 Jan 2019 19:19:52 +0000
From:   Jason Gunthorpe <jgg@...lanox.com>
To:     Logan Gunthorpe <logang@...tatee.com>
CC:     Christoph Hellwig <hch@....de>, Jerome Glisse <jglisse@...hat.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Christian Koenig <christian.koenig@....com>,
        Felix Kuehling <Felix.Kuehling@....com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <jroedel@...e.de>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>
Subject: Re: [RFC PATCH 3/5] mm/vma: add support for peer to peer to device
 vma

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..

Jason