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SubjectRe: [Qemu-devel] [RFC v2 0/2] kvm "fake DAX" device flushing
On Wed, 25 Apr 2018 16:54:12 +0530
Pankaj Gupta <pagupta@redhat.com> wrote:

[...]
> - Qemu virtio-pmem device
> It exposes a persistent memory range to KVM guest which
> at host side is file backed memory and works as persistent
> memory device. In addition to this it provides virtio
> device handling of flushing interface. KVM guest performs
> Qemu side asynchronous sync using this interface.
a random high level question,
Have you considered using a separate (from memory itself)
virtio device as controller for exposing some memory, async flushing.
And then just slaving pc-dimm devices to it with notification/ACPI
code suppressed so that guest won't touch them?

That way it might be more scale-able, you consume only 1 PCI slot
for controller vs multiple for virtio-pmem devices.


> Changes from previous RFC[1]:
>
> - Reuse existing 'pmem' code for registering persistent
> memory and other operations instead of creating an entirely
> new block driver.
> - Use VIRTIO driver to register memory information with
> nvdimm_bus and create region_type accordingly.
> - Call VIRTIO flush from existing pmem driver.
>
> Details of project idea for 'fake DAX' flushing interface is
> shared [2] & [3].
>
> Pankaj Gupta (2):
> Add virtio-pmem guest driver
> pmem: device flush over VIRTIO
>
> [1] https://marc.info/?l=linux-mm&m=150782346802290&w=2
> [2] https://www.spinics.net/lists/kvm/msg149761.html
> [3] https://www.spinics.net/lists/kvm/msg153095.html
>
> drivers/nvdimm/region_devs.c | 7 ++
> drivers/virtio/Kconfig | 12 +++
> drivers/virtio/Makefile | 1
> drivers/virtio/virtio_pmem.c | 118 +++++++++++++++++++++++++++++++++++++++
> include/linux/libnvdimm.h | 4 +
> include/uapi/linux/virtio_ids.h | 1
> include/uapi/linux/virtio_pmem.h | 58 +++++++++++++++++++
> 7 files changed, 201 insertions(+)
>

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