linux-kernel - Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory

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Message-ID: <20170418212258.GA26838@obsidianresearch.com>
Date:   Tue, 18 Apr 2017 15:22:58 -0600
From:   Jason Gunthorpe <jgunthorpe@...idianresearch.com>
To:     Dan Williams <dan.j.williams@...el.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 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?

Jason