> On Fri, Oct 12, 2018 at 10:01 PM Pankaj Gupta <pagupta@xxxxxxxxxx> wrote: > > > > This patch adds virtio-pmem driver for KVM guest. > > > > 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. > > > > This also provides function to perform guest flush over > > VIRTIO from 'pmem' driver when userspace performs flush > > on DAX memory range. > > Before we can move forward with this driver we need additional > filesystem enabling to detect when the backing device is fronting DAX > pmem or a paravirtualized page cache through virtio-pmem. Any > interface that requires fsync() and a round trip to the hypervisor to > flush host page cache is not DAX. I saw your proposal[1] for new mmap flag MAP_DIRECT. IIUIC mapping should fail for MAP_DIRECT if it requires explicit flush or buffer indirection. So, if we disable MAP_SYNC flag for virtio-pmem this should fail MAP_DIRECT as well? Otherwise without MAP_DIRECT, virtio-pmem should be defaulted to VIRTIO flush mechanism. [1] https://marc.info/?l=linux-fsdevel&m=153953206330814&w=2 Thanks, Pankaj
