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

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Message-ID: <CAPcyv4iGBT4hKrg1aSpC8ZxoXQjsC4afB4UcJu+06o954jGGAA@mail.gmail.com>
Date:   Wed, 19 Apr 2017 11:44:20 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Logan Gunthorpe <logang@...tatee.com>
Cc:     Jerome Glisse <jglisse@...hat.com>, Jens Axboe <axboe@...nel.dk>,
        Keith Busch <keith.busch@...el.com>,
        "James E.J. Bottomley" <jejb@...ux.vnet.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        linux-rdma@...r.kernel.org,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Steve Wise <swise@...ngridcomputing.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-nvme@...ts.infradead.org,
        Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
        Bjorn Helgaas <helgaas@...nel.org>, linux-pci@...r.kernel.org,
        linux-nvdimm <linux-nvdimm@...1.01.org>,
        Max Gurtovoy <maxg@...lanox.com>,
        linux-scsi <linux-scsi@...r.kernel.org>,
        Christoph Hellwig <hch@....de>
Subject: Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory

On Wed, Apr 19, 2017 at 11:41 AM, Logan Gunthorpe <logang@...tatee.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.