On 01.06.2018 14:24, Igor Mammedov wrote: > On Wed, 25 Apr 2018 16:54:12 +0530 > Pankaj Gupta <pagupta@xxxxxxxxxx> 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? I don't think slaving pc-dimm would be the right thing to do (e.g. slots, pcdimm vs nvdimm, bus(less), etc..). However the general idea is interesting for virtio-pmem (as we might have a bigger number of disks). We could have something like a virtio-pmem-bus to which you attach virtio-pmem devices. By specifying the mapping, e.g. the thread that will be used for async flushes will be implicit. > > 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(+) >> > -- Thanks, David / dhildenb
