Re: [RFC v2 1/2] virtio: add pmem driver

[Dan Williams]

[ 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@xxxxxxxxx> wrote:
> On Wed, Apr 25, 2018 at 4:24 AM, Pankaj Gupta <pagupta@xxxxxxxxxx> 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
> 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.