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From: Dan Williams <dan.j.williams@intel.com>
Date: Wed, 19 Apr 2017 11:44:20 -0700
Message-ID: <CAPcyv4iGBT4hKrg1aSpC8ZxoXQjsC4afB4UcJu+06o954jGGAA@mail.gmail.com>
Subject: Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory
To: Logan Gunthorpe <logang@deltatee.com>
Cc: Jerome Glisse <jglisse@redhat.com>, Jens Axboe <axboe@kernel.dk>,
        Keith Busch <keith.busch@intel.com>,
        "James E.J. Bottomley" <jejb@linux.vnet.ibm.com>,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        linux-rdma@vger.kernel.org,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Steve Wise <swise@opengridcomputing.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        linux-nvme@lists.infradead.org,
        Jason Gunthorpe <jgunthorpe@obsidianresearch.com>,
        Bjorn Helgaas <helgaas@kernel.org>, linux-pci@vger.kernel.org,
        linux-nvdimm <linux-nvdimm@ml01.01.org>,
        Max Gurtovoy <maxg@mellanox.com>,
        linux-scsi <linux-scsi@vger.kernel.org>,
        Christoph Hellwig <hch@lst.de>
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On Wed, Apr 19, 2017 at 11:41 AM, Logan Gunthorpe <logang@deltatee.com> wrote:
>
>
> On 19/04/17 12:30 PM, Dan Williams wrote:
>> Letting others users do the container_of() arrangement means that
>> struct page_map needs to become public and move into struct
>> dev_pagemap directly.
>
> Ah, yes, I got a bit turned around by that and failed to notice that
> page_map and dev_pagemap are different. Why is it that dev_pagemap
> contains pretty much the exact same information as page_map? The only
> thing gained that I can see is that the struct resource gains const
> protection...
>
>> ...I think that encapsulation loss is worth it for the gain of clearly
>> separating the HMM-case from the base case.
>
> Agreed.
>

Yeah, I forgot that dev_pagemap grew those fields, so we don't have
any real encapsulation today. So this would just be a pure cleanup to
kill struct page_map.