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

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Message-ID: <1492564669.25766.122.camel@kernel.crashing.org>
Date:   Wed, 19 Apr 2017 11:17:49 +1000
From:   Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:     Logan Gunthorpe <logang@...tatee.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Jerome Glisse <jglisse@...hat.com>
Cc:     Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
        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>
Subject: Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory

On Tue, 2017-04-18 at 14:48 -0600, Logan Gunthorpe wrote:
> > ...and that dma_map goes through get_dma_ops(), so I don't see the conflict?
> 
> The main conflict is in dma_map_sg which only does get_dma_ops once but
> the sg may contain memory of different types.

We can handle that in our "overriden" dma ops.

It's a bit tricky but it *could* break it down into segments and
forward portions back to the original dma ops.

Ben.