Re: [PATCH v3 00/13] virtio-fs: shared file system for virtual machines

[Miklos Szeredi <miklos@szeredi.hu>]

[Cc:  virtualization@lists.linux-foundation.org, "Michael S. Tsirkin"
<mst@redhat.com>, Jason Wang <jasowang@redhat.com>]

It'd be nice to have an ACK for this from the virtio maintainers.

Thanks,
Miklos

On Wed, Aug 21, 2019 at 7:38 PM Vivek Goyal <vgoyal@redhat.com> wrote:
>
> Hi,
>
> Here are the V3 patches for virtio-fs filesystem. This time I have
> broken the patch series in two parts. This is first part which does
> not contain DAX support. Second patch series will contain the patches
> for DAX support.
>
> I have also dropped RFC tag from first patch series as we believe its
> in good enough shape that it should get a consideration for inclusion
> upstream.
>
> These patches apply on top of 5.3-rc5 kernel and are also available
> here.
>
> https://github.com/rhvgoyal/linux/commits/vivek-5.3-aug-21-2019
>
> Patches for V1 and V2 were posted here.
>
> https://lwn.net/ml/linux-fsdevel/20181210171318.16998-1-vgoyal@redhat.com/
> http://lkml.iu.edu/hypermail/linux/kernel/1905.1/07232.html
>
> More information about the project can be found here.
>
> https://virtio-fs.gitlab.io
>
> Changes from V2
> ===============
> - Various bug fixes and performance improvements.
>
> HOWTO
> ======
> We have put instructions on how to use it here.
>
> https://virtio-fs.gitlab.io/
>
> Some Performance Numbers
> ========================
> I have basically run bunch of fio jobs to get a sense of speed of
> various operations. I wrote a simple wrapper script to run fio jobs
> 3 times and take their average and report it. These scripts are available
> here.
>
> https://github.com/rhvgoyal/virtiofs-tests
>
> I set up a directory on ramfs on host and exported that directory inside
> guest using virtio-9p and virtio-fs and ran tests inside guests. Ran
> tests with cache=none both for virtio-9p and virtio-fs so that no caching
> happens in guest. For virtio-fs, I ran an additional set of tests with
> dax enabled. Dax is not part of first patch series but I included
> results here because dax seems to get the maximum performance advantage
> and its shows the real potential of virtio-fs.
>
> Test Setup
> -----------
> - A fedora 28 host with 32G RAM, 2 sockets (6 cores per socket, 2
>   threads per core)
>
> - Using ramfs on host as backing store. 4 fio files of 2G each.
>
> - Created a VM with 16 VCPUS and 8GB memory. An 8GB cache window (for dax
>   mmap).
>
> Test Results
> ------------
> - Results in three configurations have been reported. 9p (cache=none),
>   virtio-fs (cache=none) and virtio-fs (cache=none + dax).
>
>   There are other caching modes as well but to me cache=none seemed most
>   interesting for now because it does not cache anything in guest
>   and provides strong coherence. Other modes which provide less strong
>   coherence and hence are faster are yet to be benchmarked.
>
> - Three fio ioengines psync, libaio and mmap have been used.
>
> - I/O Workload of randread, radwrite, seqread and seqwrite have been run.
>
> - Each file size is 2G. Block size 4K. iodepth=16
>
> - "multi" means same operation was done with 4 jobs and each job is
>   operating on a file of size 2G.
>
> - Some results are "0 (KiB/s)". That means that particular operation is
>   not supported in that configuration.
>
> NAME                    I/O Operation           BW(Read/Write)
>
> 9p-cache-none           seqread-psync           27(MiB/s)
> virtiofs-cache-none     seqread-psync           35(MiB/s)
> virtiofs-dax-cache-none seqread-psync           245(MiB/s)
>
> 9p-cache-none           seqread-psync-multi     117(MiB/s)
> virtiofs-cache-none     seqread-psync-multi     162(MiB/s)
> virtiofs-dax-cache-none seqread-psync-multi     894(MiB/s)
>
> 9p-cache-none           seqread-mmap            24(MiB/s)
> virtiofs-cache-none     seqread-mmap            0(KiB/s)
> virtiofs-dax-cache-none seqread-mmap            168(MiB/s)
>
> 9p-cache-none           seqread-mmap-multi      115(MiB/s)
> virtiofs-cache-none     seqread-mmap-multi      0(KiB/s)
> virtiofs-dax-cache-none seqread-mmap-multi      614(MiB/s)
>
> 9p-cache-none           seqread-libaio          26(MiB/s)
> virtiofs-cache-none     seqread-libaio          139(MiB/s)
> virtiofs-dax-cache-none seqread-libaio          160(MiB/s)
>
> 9p-cache-none           seqread-libaio-multi    129(MiB/s)
> virtiofs-cache-none     seqread-libaio-multi    142(MiB/s)
> virtiofs-dax-cache-none seqread-libaio-multi    577(MiB/s)
>
> 9p-cache-none           randread-psync          29(MiB/s)
> virtiofs-cache-none     randread-psync          34(MiB/s)
> virtiofs-dax-cache-none randread-psync          256(MiB/s)
>
> 9p-cache-none           randread-psync-multi    139(MiB/s)
> virtiofs-cache-none     randread-psync-multi    153(MiB/s)
> virtiofs-dax-cache-none randread-psync-multi    245(MiB/s)
>
> 9p-cache-none           randread-mmap           22(MiB/s)
> virtiofs-cache-none     randread-mmap           0(KiB/s)
> virtiofs-dax-cache-none randread-mmap           162(MiB/s)
>
> 9p-cache-none           randread-mmap-multi     111(MiB/s)
> virtiofs-cache-none     randread-mmap-multi     0(KiB/s)
> virtiofs-dax-cache-none randread-mmap-multi     215(MiB/s)
>
> 9p-cache-none           randread-libaio         26(MiB/s)
> virtiofs-cache-none     randread-libaio         135(MiB/s)
> virtiofs-dax-cache-none randread-libaio         157(MiB/s)
>
> 9p-cache-none           randread-libaio-multi   133(MiB/s)
> virtiofs-cache-none     randread-libaio-multi   245(MiB/s)
> virtiofs-dax-cache-none randread-libaio-multi   163(MiB/s)
>
> 9p-cache-none           seqwrite-psync          28(MiB/s)
> virtiofs-cache-none     seqwrite-psync          34(MiB/s)
> virtiofs-dax-cache-none seqwrite-psync          203(MiB/s)
>
> 9p-cache-none           seqwrite-psync-multi    128(MiB/s)
> virtiofs-cache-none     seqwrite-psync-multi    155(MiB/s)
> virtiofs-dax-cache-none seqwrite-psync-multi    717(MiB/s)
>
> 9p-cache-none           seqwrite-mmap           0(KiB/s)
> virtiofs-cache-none     seqwrite-mmap           0(KiB/s)
> virtiofs-dax-cache-none seqwrite-mmap           165(MiB/s)
>
> 9p-cache-none           seqwrite-mmap-multi     0(KiB/s)
> virtiofs-cache-none     seqwrite-mmap-multi     0(KiB/s)
> virtiofs-dax-cache-none seqwrite-mmap-multi     511(MiB/s)
>
> 9p-cache-none           seqwrite-libaio         27(MiB/s)
> virtiofs-cache-none     seqwrite-libaio         128(MiB/s)
> virtiofs-dax-cache-none seqwrite-libaio         141(MiB/s)
>
> 9p-cache-none           seqwrite-libaio-multi   119(MiB/s)
> virtiofs-cache-none     seqwrite-libaio-multi   242(MiB/s)
> virtiofs-dax-cache-none seqwrite-libaio-multi   505(MiB/s)
>
> 9p-cache-none           randwrite-psync         27(MiB/s)
> virtiofs-cache-none     randwrite-psync         34(MiB/s)
> virtiofs-dax-cache-none randwrite-psync         189(MiB/s)
>
> 9p-cache-none           randwrite-psync-multi   137(MiB/s)
> virtiofs-cache-none     randwrite-psync-multi   150(MiB/s)
> virtiofs-dax-cache-none randwrite-psync-multi   233(MiB/s)
>
> 9p-cache-none           randwrite-mmap          0(KiB/s)
> virtiofs-cache-none     randwrite-mmap          0(KiB/s)
> virtiofs-dax-cache-none randwrite-mmap          120(MiB/s)
>
> 9p-cache-none           randwrite-mmap-multi    0(KiB/s)
> virtiofs-cache-none     randwrite-mmap-multi    0(KiB/s)
> virtiofs-dax-cache-none randwrite-mmap-multi    200(MiB/s)
>
> 9p-cache-none           randwrite-libaio        25(MiB/s)
> virtiofs-cache-none     randwrite-libaio        124(MiB/s)
> virtiofs-dax-cache-none randwrite-libaio        131(MiB/s)
>
> 9p-cache-none           randwrite-libaio-multi  125(MiB/s)
> virtiofs-cache-none     randwrite-libaio-multi  241(MiB/s)
> virtiofs-dax-cache-none randwrite-libaio-multi  163(MiB/s)
>
> Conclusions
> ===========
> - In general virtio-fs seems faster than virtio-9p. Using dax makes it
>   really interesting.
>
> Note:
>   Right now dax window is 8G and max fio file size is 8G as well (4
>   files of 2G each). That means everything fits into dax window and no
>   reclaim is needed. Dax window reclaim logic is slower and if file
>   size is bigger than dax window size, performance slows down.
>
> Description from previous postings
> ==================================
>
> Design Overview
> ===============
> With the goal of designing something with better performance and local file
> system semantics, a bunch of ideas were proposed.
>
> - Use fuse protocol (instead of 9p) for communication between guest
>   and host. Guest kernel will be fuse client and a fuse server will
>   run on host to serve the requests.
>
> - For data access inside guest, mmap portion of file in QEMU address
>   space and guest accesses this memory using dax. That way guest page
>   cache is bypassed and there is only one copy of data (on host). This
>   will also enable mmap(MAP_SHARED) between guests.
>
> - For metadata coherency, there is a shared memory region which contains
>   version number associated with metadata and any guest changing metadata
>   updates version number and other guests refresh metadata on next
>   access. This is yet to be implemented.
>
> How virtio-fs differs from existing approaches
> ==============================================
> The unique idea behind virtio-fs is to take advantage of the co-location
> of the virtual machine and hypervisor to avoid communication (vmexits).
>
> DAX allows file contents to be accessed without communication with the
> hypervisor. The shared memory region for metadata avoids communication in
> the common case where metadata is unchanged.
>
> By replacing expensive communication with cheaper shared memory accesses,
> we expect to achieve better performance than approaches based on network
> file system protocols. In addition, this also makes it easier to achieve
> local file system semantics (coherency).
>
> These techniques are not applicable to network file system protocols since
> the communications channel is bypassed by taking advantage of shared memory
> on a local machine. This is why we decided to build virtio-fs rather than
> focus on 9P or NFS.
>
> Caching Modes
> =============
> Like virtio-9p, different caching modes are supported which determine the
> coherency level as well. The “cache=FOO” and “writeback” options control the
> level of coherence between the guest and host filesystems.
>
> - cache=none
>   metadata, data and pathname lookup are not cached in guest. They are always
>   fetched from host and any changes are immediately pushed to host.
>
> - cache=always
>   metadata, data and pathname lookup are cached in guest and never expire.
>
> - cache=auto
>   metadata and pathname lookup cache expires after a configured amount of time
>   (default is 1 second). Data is cached while the file is open (close to open
>   consistency).
>
> - writeback/no_writeback
>   These options control the writeback strategy.  If writeback is disabled,
>   then normal writes will immediately be synchronized with the host fs. If
>   writeback is enabled, then writes may be cached in the guest until the file
>   is closed or an fsync(2) performed. This option has no effect on mmap-ed
>   writes or writes going through the DAX mechanism.
>
> Thanks
> Vivek
>
> Miklos Szeredi (2):
>   fuse: delete dentry if timeout is zero
>   fuse: Use default_file_splice_read for direct IO
>
> Stefan Hajnoczi (6):
>   fuse: export fuse_end_request()
>   fuse: export fuse_len_args()
>   fuse: export fuse_get_unique()
>   fuse: extract fuse_fill_super_common()
>   fuse: add fuse_iqueue_ops callbacks
>   virtio_fs: add skeleton virtio_fs.ko module
>
> Vivek Goyal (5):
>   fuse: Export fuse_send_init_request()
>   Export fuse_dequeue_forget() function
>   fuse: Separate fuse device allocation and installation in fuse_conn
>   virtio-fs: Do not provide abort interface in fusectl
>   init/do_mounts.c: add virtio_fs root fs support
>
>  fs/fuse/Kconfig                 |   11 +
>  fs/fuse/Makefile                |    1 +
>  fs/fuse/control.c               |    4 +-
>  fs/fuse/cuse.c                  |    4 +-
>  fs/fuse/dev.c                   |   89 ++-
>  fs/fuse/dir.c                   |   26 +-
>  fs/fuse/file.c                  |   15 +-
>  fs/fuse/fuse_i.h                |  120 +++-
>  fs/fuse/inode.c                 |  203 +++---
>  fs/fuse/virtio_fs.c             | 1061 +++++++++++++++++++++++++++++++
>  fs/splice.c                     |    3 +-
>  include/linux/fs.h              |    2 +
>  include/uapi/linux/virtio_fs.h  |   41 ++
>  include/uapi/linux/virtio_ids.h |    1 +
>  init/do_mounts.c                |   10 +
>  15 files changed, 1462 insertions(+), 129 deletions(-)
>  create mode 100644 fs/fuse/virtio_fs.c
>  create mode 100644 include/uapi/linux/virtio_fs.h
>
> --
> 2.20.1
>