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

From: Michael S. Tsirkin
Date: Tue Sep 03 2019 - 04:31:50 EST

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On Tue, Sep 03, 2019 at 10:05:02AM +0200, Miklos Szeredi wrote:
> [Cc: virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx, "Michael S. Tsirkin"
> <mst@xxxxxxxxxx>, Jason Wang <jasowang@xxxxxxxxxx>]
>
> It'd be nice to have an ACK for this from the virtio maintainers.
>
> Thanks,
> Miklos

Can the patches themselves be posted to the relevant list(s) please?
If possible, please also include "v3" in all patches so they are
easier to find.

I poked at
https://lwn.net/ml/linux-kernel/20190821173742.24574-1-vgoyal@xxxxxxxxxx/
specifically
https://lwn.net/ml/linux-kernel/20190821173742.24574-12-vgoyal@xxxxxxxxxx/
and things like:
+ /* TODO lock */
give me pause.

Cleanup generally seems broken to me - what pauses the FS

What about the rest of TODOs in that file?

use of usleep is hacky - can't we do better e.g. with a
completion?

Some typos - e.g. "reuests".

>
> On Wed, Aug 21, 2019 at 7:38 PM Vivek Goyal <vgoyal@xxxxxxxxxx> 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@xxxxxxxxxx/
> > 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 âcache=FOOâ and âwritebackâ 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

Don't the new files need a MAINTAINERS entry?
I think we want virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx to be
copied.

> >
> > --
> > 2.20.1
> >

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