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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: Logan Gunthorpe <logang@deltatee.com>,
        Dan Williams
	 <dan.j.williams@intel.com>
Cc: Bjorn Helgaas <helgaas@kernel.org>,
        Jason Gunthorpe
 <jgunthorpe@obsidianresearch.com>,
        Christoph Hellwig <hch@lst.de>, Sagi
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        "James E.J. Bottomley"
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        "Martin K. Petersen"
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        Jens Axboe <axboe@kernel.dk>,
        Steve Wise
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        Stephen Bates <sbates@raithlin.com>, Max
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        Keith Busch <keith.busch@intel.com>, linux-pci@vger.kernel.org,
        linux-scsi <linux-scsi@vger.kernel.org>,
        linux-nvme@lists.infradead.org, linux-rdma@vger.kernel.org,
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        Jerome Glisse <jglisse@redhat.com>
Date: Mon, 17 Apr 2017 08:32:38 +1000
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On Sun, 2017-04-16 at 10:47 -0600, Logan Gunthorpe wrote:
> > I think you need to give other archs a chance to support this with a
> > design that considers the offset case as a first class citizen rather
> > than an afterthought.
> 
> I'll consider this. Given the fact I can use your existing
> get_dev_pagemap infrastructure to look up the p2pmem device this
> probably isn't as hard as I thought it would be anyway (we probably
> don't even need a page flag). We'd just have lookup the dev_pagemap,
> test if it's a p2pmem device, and if so, call a p2pmem_dma_map function
> which could apply the offset or do any other arch specific logic (if
> necessary).

I'm still not 100% why do you need a "p2mem device" mind you ...

Cheers,
Ben.