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From: Dan Williams <dan.j.williams@intel.com>
Date: Wed, 25 Apr 2018 07:21:21 -0700
Message-ID: <CAPcyv4hvrB08XPTbVK0xT2_1Xmaid=-v3OMxJVDTNwQucsOHLA@mail.gmail.com>
Subject: Re: [RFC v2 1/2] virtio: add pmem driver
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Sender: owner-linux-mm@kvack.org
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To: Pankaj Gupta <pagupta@redhat.com>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, KVM list <kvm@vger.kernel.org>, Qemu Developers <qemu-devel@nongnu.org>, linux-nvdimm <linux-nvdimm@ml01.01.org>, Linux MM <linux-mm@kvack.org>, Jan Kara <jack@suse.cz>, Stefan Hajnoczi <stefanha@redhat.com>, Rik van Riel <riel@surriel.com>, Haozhong Zhang <haozhong.zhang@intel.com>, Nitesh Narayan Lal <nilal@redhat.com>, Kevin Wolf <kwolf@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, "Zwisler, Ross" <ross.zwisler@intel.com>, David Hildenbrand <david@redhat.com>, Xiao Guangrong <xiaoguangrong.eric@gmail.com>, Christoph Hellwig <hch@infradead.org>, Marcel Apfelbaum <marcel@redhat.com>, "Michael S. Tsirkin" <mst@redhat.com>, niteshnarayanlal@hotmail.com, Igor Mammedov <imammedo@redhat.com>, lcapitulino@redhat.com

On Wed, Apr 25, 2018 at 4:24 AM, Pankaj Gupta <pagupta@redhat.com> 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.