From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pankaj Gupta Subject: Re: [Qemu-devel] [PATCH v2 2/2] virtio-pmem: Add virtio pmem driver Date: Wed, 17 Oct 2018 15:11:49 -0400 (EDT) Message-ID: <431127218.21694133.1539803509205.JavaMail.zimbra@redhat.com> References: <20181013050021.11962-1-pagupta@redhat.com> <20181013050021.11962-3-pagupta@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: Kevin Wolf , Nitesh Narayan Lal , Jan Kara , Xiao Guangrong , KVM list , Rik van Riel , linux-nvdimm , David Hildenbrand , Linux Kernel Mailing List , Qemu Developers , Christoph Hellwig , Igor Mammedov , Paolo Bonzini , "Michael S. Tsirkin" , Stefan Hajnoczi , zwisler-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, lcapitulino-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org To: Dan Williams Return-path: In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linux-nvdimm-bounces-hn68Rpc1hR1g9hUCZPvPmw@public.gmane.org Sender: "Linux-nvdimm" List-Id: kvm.vger.kernel.org > On Fri, Oct 12, 2018 at 10:01 PM Pankaj Gupta 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