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From:   Amir Goldstein <amir73il@gmail.com>
Date:   Wed, 11 Mar 2020 07:22:51 +0200
Message-ID: <CAOQ4uxi_Xrf+iyP6KVugFgLOfzUvscMr0de0KxQo+jHNBCA9oA@mail.gmail.com>
Subject: Re: [PATCH 00/20] virtiofs: Add DAX support
To:     Vivek Goyal <vgoyal@redhat.com>
Cc:     linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        linux-nvdimm <linux-nvdimm@lists.01.org>, virtio-fs@redhat.com,
        Miklos Szeredi <miklos@szeredi.hu>,
        Stefan Hajnoczi <stefanha@redhat.com>,
        "Dr. David Alan Gilbert" <dgilbert@redhat.com>, mst@redhat.com
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On Wed, Mar 4, 2020 at 7:01 PM Vivek Goyal <vgoyal@redhat.com> wrote:
>
> Hi,
>
> This patch series adds DAX support to virtiofs filesystem. This allows
> bypassing guest page cache and allows mapping host page cache directly
> in guest address space.
>
> When a page of file is needed, guest sends a request to map that page
> (in host page cache) in qemu address space. Inside guest this is
> a physical memory range controlled by virtiofs device. And guest
> directly maps this physical address range using DAX and hence gets
> access to file data on host.
>
> This can speed up things considerably in many situations. Also this
> can result in substantial memory savings as file data does not have
> to be copied in guest and it is directly accessed from host page
> cache.
>
> Most of the changes are limited to fuse/virtiofs. There are couple
> of changes needed in generic dax infrastructure and couple of changes
> in virtio to be able to access shared memory region.
>
> These patches apply on top of 5.6-rc4 and are also available here.
>
> https://github.com/rhvgoyal/linux/commits/vivek-04-march-2020
>
> Any review or feedback is welcome.
>
[...]
>  drivers/dax/super.c                |    3 +-
>  drivers/virtio/virtio_mmio.c       |   32 +
>  drivers/virtio/virtio_pci_modern.c |  107 +++
>  fs/dax.c                           |   66 +-
>  fs/fuse/dir.c                      |    2 +
>  fs/fuse/file.c                     | 1162 +++++++++++++++++++++++++++-

That's a big addition to already big file.c.
Maybe split dax specific code to dax.c?
Can be a post series cleanup too.

Thanks,
Amir.