linux-kernel - Re: [PATCH v2 0/2] kvm "fake DAX" device

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Date:   Sat, 13 Oct 2018 09:06:07 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Pankaj Gupta <pagupta@...hat.com>
Cc:     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>, Jan Kara <jack@...e.cz>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        Rik van Riel <riel@...riel.com>,
        Nitesh Narayan Lal <nilal@...hat.com>,
        Kevin Wolf <kwolf@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>, zwisler@...nel.org,
        Vishal L Verma <vishal.l.verma@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        David Hildenbrand <david@...hat.com>,
        Xiao Guangrong <xiaoguangrong.eric@...il.com>,
        Christoph Hellwig <hch@...radead.org>,
        "Michael S. Tsirkin" <mst@...hat.com>, lcapitulino@...hat.com,
        Igor Mammedov <imammedo@...hat.com>,
        Eric Blake <eblake@...hat.com>
Subject: Re: [PATCH v2 0/2] kvm "fake DAX" device

On Fri, Oct 12, 2018 at 10:00 PM Pankaj Gupta <pagupta@...hat.com> wrote:
>
>  This patch series has implementation for "fake DAX".
>  "fake DAX" is fake persistent memory(nvdimm) in guest
>  which allows to bypass the guest page cache. This also
>  implements a VIRTIO based asynchronous flush mechanism.

Can we stop calling this 'fake DAX', because it isn't 'DAX' and it's
starting to confuse people. This enabling is effectively a
host-page-cache-passthrough mechanism not DAX. Let's call the whole
approach virtio-pmem, and leave DAX out of the name to hopefully
prevent people from wondering why some DAX features are disabled with
this driver. For example MAP_SYNC is not compatible with this
approach.

Additional enabling is need to disable MAP_SYNC in the presence of a
virtio-pmem device. See the rough proposal here:

    https://lkml.org/lkml/2018/4/25/756