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Re: [Qemu-devel] [PATCH v3 00/16] vhost-user: add migration log support
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [PATCH v3 00/16] vhost-user: add migration log support (for 2.5) |
Date: |
Wed, 16 Sep 2015 17:46:35 +0300 |
On Thu, Aug 06, 2015 at 02:40:36PM +0200, address@hidden wrote:
> From: Marc-André Lureau <address@hidden>
>
> Hi,
>
> The following series implement shareable log for vhost-user to support
> memory tracking during live migration. On qemu-side, the solution is
> fairly straightfoward since vhost already supports the dirty log, only
> vhost-user couldn't access the log memory until then.
>
> The series is based on top of "protocol feature negotiation" series
> proposed earlier by Michael S. Tsirkinm and "vhost user: Add live
> migration" series from Thibaut Collet .
I've been thinking about this. I wonder whether an alternative
approach would make sense.
Specifically, write protect the pages we want to track in host
PTEs; on a page fault, log the change (in kernel) and restart.
This could work for all of vhost, userspace qemu, vhost-user
transparently (so we don't need to teach dpdk to do
dirty logging).
It would be more robust since it removes the ability for
a buggy userspace to change memory without logging it.
And it would be faster since log is only set on the 1st
write, afterwards page is writeable - so no fault.
It's a kernel patch so more work.
I guess we can support both approaches (e.g. for old kernels)
but I thought I'd through this out there.
> Since v2:
> - changed some patch summary
> - added migration tests
> - added a patch to replace error message with a trace
>
> The development branch I used is:
> https://github.com/elmarco/qemu branch "vhost-user"
>
> More comments welcome!
>
> Marc-André Lureau (16):
> configure: probe for memfd
> util: add linux-only memfd fallback
> util: add memfd helpers
> vhost: alloc shareable log
> vhost: document log resizing
> vhost: use variable arguments for vhost_call()
> vhost-user: start and end the va_list
> vhost-user: send log shm fd along with log_base
> vhost-user: document migration log
> net: add trace_vhost_user_event
> vhost-user-test: move wait_for_fds() out
> vhost-user-test: remove useless static check
> vhost-user-test: wrap server in TestServer struct
> vhost-user-test: learn to tweak various qemu arguments
> vhost-user-test: add live-migration test
> vhost-user-test: check ownership during migration
>
> configure | 19 ++
> docs/specs/vhost-user.txt | 42 +++++
> hw/virtio/vhost-backend.c | 4 +-
> hw/virtio/vhost-user.c | 52 ++++--
> hw/virtio/vhost.c | 45 ++++-
> include/hw/virtio/vhost-backend.h | 6 +-
> include/hw/virtio/vhost.h | 3 +-
> include/qemu/memfd.h | 24 +++
> net/vhost-user.c | 5 +-
> tests/vhost-user-test.c | 366
> +++++++++++++++++++++++++++++++-------
> trace-events | 3 +
> util/Makefile.objs | 2 +-
> util/memfd.c | 126 +++++++++++++
> 13 files changed, 602 insertions(+), 95 deletions(-)
> create mode 100644 include/qemu/memfd.h
> create mode 100644 util/memfd.c
>
> --
> 2.4.3