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Date:   Thu, 27 Jun 2019 11:01:54 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Logan Gunthorpe <logang@deltatee.com>
Cc:     Christoph Hellwig <hch@lst.de>, linux-kernel@vger.kernel.org,
        linux-block@vger.kernel.org, linux-nvme@lists.infradead.org,
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        Jens Axboe <axboe@kernel.dk>,
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        Dan Williams <dan.j.williams@intel.com>,
        Sagi Grimberg <sagi@grimberg.me>,
        Keith Busch <kbusch@kernel.org>,
        Jason Gunthorpe <jgg@ziepe.ca>,
        Stephen Bates <sbates@raithlin.com>
Subject: Re: [RFC PATCH 00/28] Removing struct page from P2PDMA
Message-ID: <20190627090154.GA11548@lst.de>
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On Wed, Jun 26, 2019 at 12:31:08PM -0600, Logan Gunthorpe wrote:
> > we have a hole behind len where we could store flag.  Preferably
> > optionally based on a P2P or other magic memory types config
> > option so that 32-bit systems with 32-bit phys_addr_t actually
> > benefit from the smaller and better packing structure.
> 
> That seems sensible. The one thing that's unclear though is how to get
> the PCI Bus address when appropriate. Can we pass that in instead of the
> phys_addr with an appropriate flag? Or will we need to pass the actual
> physical address and then, at the map step, the driver has to some how
> lookup the PCI device to figure out the bus offset?

Yes, I think we'll need a lookup mechanism of some kind.