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Subject: Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>,
        Dan Williams <dan.j.williams@intel.com>
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Date: Wed, 19 Apr 2017 11:21:50 +1000
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On Tue, 2017-04-18 at 15:22 -0600, Jason Gunthorpe wrote:
> On Tue, Apr 18, 2017 at 02:11:33PM -0700, Dan Williams wrote:
> > > I think this opens an even bigger can of worms..
> > 
> > No, I don't think it does. You'd only shim when the target page is
> > backed by a device, not host memory, and you can figure this out by
> > a
> > is_zone_device_page()-style lookup.
> 
> The bigger can of worms is how do you meaningfully stack dma_ops.
> 
> What does the p2p provider do when it detects a p2p page?

Yeah I think we don't really want to stack dma_ops... thinking more
about it.

As I just wrote, it looks like we might need a more specialised hook
in the devmap to be used by the main dma_op, on a per-page basis.

Ben.