Re: [RFC 5/8] scatterlist: Modify SG copy functions to support io memory.

From	Logan Gunthorpe <logang@deltatee.com>
Newsgroups	linux.kernel
Subject	Re: [RFC 5/8] scatterlist: Modify SG copy functions to support io memory.
Date	2017-04-04 00:20 +0200
Message-ID	<tsiul-4rW-5@gated-at.bofh.it> (permalink)
References	(1 earlier) <tqQAb-4sB-31@gated-at.bofh.it> <tqZ0J-1qH-9@gated-at.bofh.it> <tr6Yh-6ua-3@gated-at.bofh.it> <tshHY-3Tw-19@gated-at.bofh.it> <tsi1j-40v-9@gated-at.bofh.it>
Organization	linux.* mail to news gateway

Show all headers | View raw


On 03/04/17 03:44 PM, Dan Williams wrote:
> On Mon, Apr 3, 2017 at 2:20 PM, Logan Gunthorpe <logang@deltatee.com> wrote:
>> Hi Christoph,
>>
>> What are your thoughts on an approach like the following untested
>> draft patch.
>>
>> The patch (if fleshed out) makes it so iomem can be used in an sgl
>> and WARN_ONs will occur in places where drivers attempt to access
>> iomem directly through the sgl.
>>
>> I'd also probably create a p2pmem_alloc_sgl helper function so driver
>> writers wouldn't have to mess with sg_set_iomem_page.
>>
>> With all that in place, it should be relatively safe for drivers to
>> implement p2pmem even though we'd still technically be violating the
>> __iomem boundary in some places.
> 
> Just reacting to this mail, I still haven't had a chance to take a
> look at the rest of the series.
> 
> The pfn_t type was invented to carry extra type and page lookup
> information about the memory behind a given pfn. At first glance that
> seems a more natural place to carry an indication that this is an
> "I/O" pfn.

I agree... But what are the plans for pfn_t? Is anyone working on using
it in the scatterlist code? Currently it's not there yet and given the
assertion that we will continue to be using struct page for DMA is that
a direction we'd want to go?

Logan

Thread

[RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Logan Gunthorpe <logang@deltatee.com> - 2017-03-31 00:20 +0200
  [RFC 1/8] Introduce Peer-to-Peer memory (p2pmem) device Logan Gunthorpe <logang@deltatee.com> - 2017-03-31 00:20 +0200
    Re: [RFC 1/8] Introduce Peer-to-Peer memory (p2pmem) device Sinan Kaya <okaya@codeaurora.org> - 2017-03-31 20:50 +0200
      Re: [RFC 1/8] Introduce Peer-to-Peer memory (p2pmem) device Logan Gunthorpe <logang@deltatee.com> - 2017-03-31 23:30 +0200
        Re: [RFC 1/8] Introduce Peer-to-Peer memory (p2pmem) device Sinan Kaya <okaya@codeaurora.org> - 2017-03-31 23:40 +0200
          Re: [RFC 1/8] Introduce Peer-to-Peer memory (p2pmem) device Logan Gunthorpe <logang@deltatee.com> - 2017-04-01 00:50 +0200
            Re: [RFC 1/8] Introduce Peer-to-Peer memory (p2pmem) device Sinan Kaya <okaya@codeaurora.org> - 2017-04-01 02:00 +0200
              Re: [RFC 1/8] Introduce Peer-to-Peer memory (p2pmem) device Logan Gunthorpe <logang@deltatee.com> - 2017-04-01 04:00 +0200
                Re: [RFC 1/8] Introduce Peer-to-Peer memory (p2pmem) device okaya@codeaurora.org - 2017-04-01 04:20 +0200
                Re: [RFC 1/8] Introduce Peer-to-Peer memory (p2pmem) device Logan Gunthorpe <logang@deltatee.com> - 2017-04-02 00:20 +0200
                Re: [RFC 1/8] Introduce Peer-to-Peer memory (p2pmem) device Sinan Kaya <okaya@codeaurora.org> - 2017-04-02 04:30 +0200
                Re: [RFC 1/8] Introduce Peer-to-Peer memory (p2pmem) device Logan Gunthorpe <logang@deltatee.com> - 2017-04-02 19:30 +0200
                Re: [RFC 1/8] Introduce Peer-to-Peer memory (p2pmem) device Sinan Kaya <okaya@codeaurora.org> - 2017-04-02 23:10 +0200
                Re: [RFC 1/8] Introduce Peer-to-Peer memory (p2pmem) device Logan Gunthorpe <logang@deltatee.com> - 2017-04-03 06:30 +0200
  [RFC 4/8] p2pmem: Add debugfs "stats" file Logan Gunthorpe <logang@deltatee.com> - 2017-03-31 00:20 +0200
    Re: [RFC 4/8] p2pmem: Add debugfs "stats" file Sagi Grimberg <sagi@grimberg.me> - 2017-04-04 12:50 +0200
      Re: [RFC 4/8] p2pmem: Add debugfs "stats" file Logan Gunthorpe <logang@deltatee.com> - 2017-04-04 19:30 +0200
      RE: [RFC 4/8] p2pmem: Add debugfs "stats" file "Steve Wise" <swise@opengridcomputing.com> - 2017-04-05 18:20 +0200
  [RFC 2/8] cxgb4: setup pcie memory window 4 and create p2pmem region Logan Gunthorpe <logang@deltatee.com> - 2017-03-31 00:20 +0200
    Re: [RFC 2/8] cxgb4: setup pcie memory window 4 and create p2pmem  region Sagi Grimberg <sagi@grimberg.me> - 2017-04-04 12:50 +0200
      Re: [RFC 2/8] cxgb4: setup pcie memory window 4 and create p2pmem  region Logan Gunthorpe <logang@deltatee.com> - 2017-04-04 18:00 +0200
      RE: [RFC 2/8] cxgb4: setup pcie memory window 4 and create p2pmem region "Steve Wise" <swise@opengridcomputing.com> - 2017-04-05 18:20 +0200
  [RFC 5/8] scatterlist: Modify SG copy functions to support io memory. Logan Gunthorpe <logang@deltatee.com> - 2017-03-31 00:20 +0200
    Re: [RFC 5/8] scatterlist: Modify SG copy functions to support io  memory. Christoph Hellwig <hch@infradead.org> - 2017-03-31 09:20 +0200
      Re: [RFC 5/8] scatterlist: Modify SG copy functions to support io  memory. Logan Gunthorpe <logang@deltatee.com> - 2017-03-31 17:50 +0200
        Re: [RFC 5/8] scatterlist: Modify SG copy functions to support io  memory. Logan Gunthorpe <logang@deltatee.com> - 2017-04-03 23:30 +0200
          Re: [RFC 5/8] scatterlist: Modify SG copy functions to support io memory. Dan Williams <dan.j.williams@intel.com> - 2017-04-03 23:50 +0200
            Re: [RFC 5/8] scatterlist: Modify SG copy functions to support io  memory. Logan Gunthorpe <logang@deltatee.com> - 2017-04-04 00:20 +0200
              Re: [RFC 5/8] scatterlist: Modify SG copy functions to support io memory. Dan Williams <dan.j.williams@intel.com> - 2017-04-04 00:50 +0200
                Re: [RFC 5/8] scatterlist: Modify SG copy functions to support io  memory. Logan Gunthorpe <logang@deltatee.com> - 2017-04-04 01:20 +0200
                Re: [RFC 5/8] scatterlist: Modify SG copy functions to support io memory. Dan Williams <dan.j.williams@intel.com> - 2017-04-04 02:10 +0200
                Re: [RFC 5/8] scatterlist: Modify SG copy functions to support io  memory. Logan Gunthorpe <logang@deltatee.com> - 2017-04-07 20:00 +0200
  [RFC 8/8] p2pmem: Added char device user interface Logan Gunthorpe <logang@deltatee.com> - 2017-03-31 00:20 +0200
  [RFC 7/8] p2pmem: Support device removal Logan Gunthorpe <logang@deltatee.com> - 2017-03-31 00:20 +0200

csiph-web