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    SubjectRe: Enabling peer to peer device transactions for PCIe devices
    On Tue, Nov 22, 2016 at 10:59 AM, Serguei Sagalovitch
    <serguei.sagalovitch@amd.com> wrote:
    > Dan,
    >
    > I personally like "device-DAX" idea but my concerns are:
    >
    > - How well it will co-exists with the DRM infrastructure / implementations
    > in part dealing with CPU pointers?

    Inside the kernel a device-DAX range is "just memory" in the sense
    that you can perform pfn_to_page() on it and issue I/O, but the vma is
    not migratable. To be honest I do not know how well that co-exists
    with drm infrastructure.

    > - How well we will be able to handle case when we need to "move"/"evict"
    > memory/data to the new location so CPU pointer should point to the new
    > physical location/address
    > (and may be not in PCI device memory at all)?

    So, device-DAX deliberately avoids support for in-kernel migration or
    overcommit. Those cases are left to the core mm or drm. The device-dax
    interface is for cases where all that is needed is a direct-mapping to
    a statically-allocated physical-address range be it persistent memory
    or some other special reserved memory range.

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