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From:   Dan Williams <dan.j.williams@intel.com>
Date:   Wed, 25 Apr 2018 07:43:52 -0700
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Subject: Re: [RFC v2 1/2] virtio: add pmem driver
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, jmoyer <jmoyer@redhat.com>
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[ 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@intel.com> wrote:
> 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.