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    SubjectRe: [RFC v2 1/2] virtio: add pmem driver
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    Dan Williams <dan.j.williams@intel.com> writes:

    > [ adding Jeff directly since he has also been looking at
    > infrastructure to track when MAP_SYNC should be disabled ]
    >
    > On Wed, Apr 25, 2018 at 7:21 AM, Dan Williams <dan.j.williams@intel.com> wrote:
    >> On Wed, Apr 25, 2018 at 4:24 AM, Pankaj Gupta <pagupta@redhat.com> wrote:
    >>> This patch adds virtio-pmem driver for KVM
    >>> guest.
    >>
    >> Minor nit, please expand your changelog line wrapping to 72 columns.
    >>
    >>>
    >>> Guest reads the persistent memory range
    >>> information from Qemu over VIRTIO and registers
    >>> it on nvdimm_bus. It also creates a nd_region
    >>> object with the persistent memory range
    >>> information so that existing 'nvdimm/pmem'
    >>> driver can reserve this into system memory map.
    >>> This way 'virtio-pmem' driver uses existing
    >>> functionality of pmem driver to register persistent
    >>> memory compatible for DAX capable filesystems.
    >>
    >> We need some additional enabling to disable MAP_SYNC for this

    enable to disable... I like it! ;-)

    >> configuration. In other words, if fsync() is required then we must
    >> disable the MAP_SYNC optimization. I think this should be a struct
    >> dax_device property looked up at mmap time in each MAP_SYNC capable
    >> ->mmap() file operation implementation.

    Ideally, qemu (seabios?) would advertise a platform capabilities
    sub-table that doesn't fill in the flush bits.

    -Jeff

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