Re: [RFC 2/2] KVM: add virtio-pmem driver

[Rik van Riel]

On Thu, 2017-10-12 at 18:18 -0400, Pankaj Gupta wrote:
> > 
> > On Thu, Oct 12, 2017 at 2:25 PM, Pankaj Gupta <pagupta@xxxxxxxxxx>
> > wrote:
> > > 
> > > > > Â This patch adds virtio-pmem driver for KVM guest.
> > > > > Â Guest reads the persistent memory range information
> > > > > Â over virtio bus from Qemu and reserves the range
> > > > > Â as persistent memory. Guest also allocates a block
> > > > > Â device corresponding to the pmem range which later
> > > > > Â can be accessed with DAX compatible file systems.
> > > > > Â Idea is to use the virtio channel between guest and
> > > > > Â host to perform the block device flush for guest pmem
> > > > > Â DAX device.
> > > > > 
> > > > > Â There is work to do including DAX file system support
> > > > > Â and other advanced features.
> > > > > 
> > > > > Signed-off-by: Pankaj Gupta <pagupta@xxxxxxxxxx>
> > > > > ---
> > > > > Âdrivers/virtio/KconfigÂÂÂÂÂÂÂÂÂÂÂ|ÂÂ10 ++
> > > > > Âdrivers/virtio/MakefileÂÂÂÂÂÂÂÂÂÂ|ÂÂÂ1 +
> > > > > Âdrivers/virtio/virtio_pmem.cÂÂÂÂÂ| 322
> > > > > Â+++++++++++++++++++++++++++++++++++++++
> > > > > Âinclude/uapi/linux/virtio_pmem.h |ÂÂ55 +++++++
> > > > > Â4 files changed, 388 insertions(+)
> > > > > Âcreate mode 100644 drivers/virtio/virtio_pmem.c
> > > > > Âcreate mode 100644 include/uapi/linux/virtio_pmem.h
> > > > > 
> > > > > diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig
> > > > > index cff773f15b7e..0192c4bda54b 100644
> > > > > --- a/drivers/virtio/Kconfig
> > > > > +++ b/drivers/virtio/Kconfig
> > > > > @@ -38,6 +38,16 @@ config VIRTIO_PCI_LEGACY
> > > > > 
> > > > > ÂÂÂÂÂÂÂÂÂÂIf unsure, say Y.
> > > > > 
> > > > > +config VIRTIO_PMEM
> > > > > +ÂÂÂÂÂÂÂtristate "Virtio pmem driver"
> > > > > +ÂÂÂÂÂÂÂdepends on VIRTIO
> > > > > +ÂÂÂÂÂÂÂ---help---
> > > > > +ÂÂÂÂÂÂÂÂThis driver adds persistent memory range within a
> > > > > KVM guest.

With "Virtio Block Backed Pmem" we could name the config
option VIRTIO_BLOCK_PMEM

The documentation text could make it clear to people that the
image shows up as a disk image on the host, but as a pmem
memory range in the guest.

> > > > I think we need to call this something other than persistent
> > > > memory to
> > > > make it clear that this not memory where the persistence can be
> > > > managed from userspace. The persistence point always requires
> > > > 
> > So currently /proc/iomem in a guest with a pmem device attached to
> > a
> > namespace looks like this:
> > 
> > ÂÂÂÂc00000000-13bfffffff : Persistent Memory
> > ÂÂÂÂÂÂÂc00000000-13bfffffff : namespace2.0
> > 
> > Can we call it "Virtio Shared Memory" to make it clear it is a
> > different beast than typical "Persistent Memory"?ÂÂYou can likely
> 
> I think somewhere we need persistent keyword 'Virtio Persistent
> Memory' orÂ
> so.

Still hoping for better ideas than "Virtio Block Backed Pmem" :)