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

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Message-ID: <x49o9i6885e.fsf@segfault.boston.devel.redhat.com>
Date:   Thu, 26 Apr 2018 08:27:41 -0400
From:   Jeff Moyer <jmoyer@...hat.com>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     Pankaj Gupta <pagupta@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        KVM list <kvm@...r.kernel.org>,
        Qemu Developers <qemu-devel@...gnu.org>,
        linux-nvdimm <linux-nvdimm@...1.01.org>,
        Linux MM <linux-mm@...ck.org>, Jan Kara <jack@...e.cz>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        Rik van Riel <riel@...riel.com>,
        Haozhong Zhang <haozhong.zhang@...el.com>,
        Nitesh Narayan Lal <nilal@...hat.com>,
        Kevin Wolf <kwolf@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        "Zwisler\, Ross" <ross.zwisler@...el.com>,
        David Hildenbrand <david@...hat.com>,
        Xiao Guangrong <xiaoguangrong.eric@...il.com>,
        Christoph Hellwig <hch@...radead.org>,
        Marcel Apfelbaum <marcel@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        niteshnarayanlal@...mail.com, Igor Mammedov <imammedo@...hat.com>,
        lcapitulino@...hat.com
Subject: Re: [RFC v2 1/2] virtio: add pmem driver

Dan Williams <dan.j.williams@...el.com> writes:

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

enable to disable... I like it!  ;-)

>> 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.

Ideally, qemu (seabios?) would advertise a platform capabilities
sub-table that doesn't fill in the flush bits.

-Jeff