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Message-ID: <CAPcyv4g5ifbpukthMXMro8qKdfoXAhftDpiwWWFCLZ4dK8JnnA@mail.gmail.com>
Date: Tue, 18 Apr 2017 14:36:06 -0700
From: Dan Williams <dan.j.williams@...el.com>
To: Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Cc: Logan Gunthorpe <logang@...tatee.com>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Bjorn Helgaas <helgaas@...nel.org>,
Christoph Hellwig <hch@....de>,
Sagi Grimberg <sagi@...mberg.me>,
"James E.J. Bottomley" <jejb@...ux.vnet.ibm.com>,
"Martin K. Petersen" <martin.petersen@...cle.com>,
Jens Axboe <axboe@...nel.dk>,
Steve Wise <swise@...ngridcomputing.com>,
Stephen Bates <sbates@...thlin.com>,
Max Gurtovoy <maxg@...lanox.com>,
Keith Busch <keith.busch@...el.com>, linux-pci@...r.kernel.org,
linux-scsi <linux-scsi@...r.kernel.org>,
linux-nvme@...ts.infradead.org, linux-rdma@...r.kernel.org,
linux-nvdimm <linux-nvdimm@...1.01.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Jerome Glisse <jglisse@...hat.com>
Subject: Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory
On Tue, Apr 18, 2017 at 2:22 PM, Jason Gunthorpe
<jgunthorpe@...idianresearch.com> 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.
This goes back to my original comment to make this capability a
function of the pci bridge itself. The kernel has an implementation of
a dynamically created bridge device that injects its own dma_ops for
the devices behind the bridge. See vmd_setup_dma_ops() in
drivers/pci/host/vmd.c.
> What does the p2p provider do when it detects a p2p page?
Check to see if the arch requires this offset translation that Ben
brought up and if not provide the physical address as the patches are
doing now.
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