Re: [PATCH 0/3] migration: Add COLO multifd support and COLO migration unit test

[Peter Xu <peterx@redhat.com>]

On Tue, Dec 30, 2025 at 03:05:43PM +0100, Lukas Straub wrote:
> Hello everyone,
> This adds COLO multifd support and migration unit tests for COLO migration
> and failover.

Hi, Lukas,

I'll review the series after the new year.

Could you still introduce some background on how you're deploying COLO?  Do
you use it in production, or for fun?

COLO is still a nice and interesting feature, said that, COLO has quite a
lot of code plugged into migration core.  I wished it's like a multifd
compressor which was much more self-contained, but it's not.  I wished we
can simplify the code in QEMU migration.

We've talked it through before with current COLO maintainers, it looks to
me there aren't really much users using it in production, meanwhile COLO
doesn't look like a feature to benefit individual QEMU users either.

I want to study the use case of COLO in status quo, and evaluate how much
effort we should put on it in the future.  Note that if it's for fun we can
always use a stable branch which will be there forever.  We'll need to
think about QEMU evolving in the future, and what's best for QEMU.

Thanks,

> 
> Regards,
> Lukas
> 
> Signed-off-by: Lukas Straub <lukasstraub2@web.de>
> ---
> Lukas Straub (3):
>       multifd: Add colo support
>       migration-test: Add -snapshot option for COLO
>       migration-test: Add COLO migration unit test
> 
>  migration/meson.build              |   2 +-
>  migration/multifd-colo.c           |  57 ++++++++++++++++++
>  migration/multifd-colo.h           |  26 +++++++++
>  migration/multifd.c                |  14 ++++-
>  tests/qtest/meson.build            |   7 ++-
>  tests/qtest/migration-test.c       |   1 +
>  tests/qtest/migration/colo-tests.c | 115 +++++++++++++++++++++++++++++++++++++
>  tests/qtest/migration/framework.c  |  69 +++++++++++++++++++++-
>  tests/qtest/migration/framework.h  |  10 ++++
>  9 files changed, 294 insertions(+), 7 deletions(-)
> ---
> base-commit: 942b0d378a1de9649085ad6db5306d5b8cef3591
> change-id: 20251230-colo_unit_test_multifd-8bf58dcebd46
> 
> Best regards,
> -- 
> Lukas Straub <lukasstraub2@web.de>
> 

-- 
Peter Xu