linux-kernel - Re: [PATCH v5 01/13] PCI/P2PDMA: Support peer-to-peer memory

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Date:   Fri, 31 Aug 2018 09:48:40 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Christian König <christian.koenig@....com>,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-nvme@...ts.infradead.org, linux-rdma@...r.kernel.org,
        linux-nvdimm@...ts.01.org, linux-block@...r.kernel.org
Cc:     Stephen Bates <sbates@...thlin.com>,
        Christoph Hellwig <hch@....de>,
        Keith Busch <keith.busch@...el.com>,
        Sagi Grimberg <sagi@...mberg.me>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Jason Gunthorpe <jgg@...lanox.com>,
        Max Gurtovoy <maxg@...lanox.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Alex Williamson <alex.williamson@...hat.com>
Subject: Re: [PATCH v5 01/13] PCI/P2PDMA: Support peer-to-peer memory



On 31/08/18 02:04 AM, Christian König wrote:
> Am 30.08.2018 um 20:53 schrieb Logan Gunthorpe:
>> Some PCI devices may have memory mapped in a BAR space that's
>> intended for use in peer-to-peer transactions. In order to enable
>> such transactions the memory must be registered with ZONE_DEVICE pages
>> so it can be used by DMA interfaces in existing drivers.
> 
> We want to use that feature without ZONE_DEVICE pages for DMA-buf as well.
> 
> How hard would it be to separate enabling P2P detection (e.g. distance 
> between two devices) from this?

Pretty easy. P2P detection is pretty much just pci_p2pdma_distance() ,
which has nothing to do with the ZONE_DEVICE support.

(And the distance function makes use of a number of static functions
which could be combined into a simpler interface, should we need it.)

Logan