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Re: [PATCH-for-9.1 v2 2/3] migration: Remove RDMA protocol handling


From: Thomas Huth
Subject: Re: [PATCH-for-9.1 v2 2/3] migration: Remove RDMA protocol handling
Date: Thu, 28 Mar 2024 16:22:27 +0100
User-agent: Mozilla Thunderbird

On 28/03/2024 16.01, Peter Xu wrote:
On Thu, Mar 28, 2024 at 11:18:04AM -0300, Fabiano Rosas wrote:
Philippe Mathieu-Daudé <philmd@linaro.org> writes:

The whole RDMA subsystem was deprecated in commit e9a54265f5
("hw/rdma: Deprecate the pvrdma device and the rdma subsystem")
released in v8.2.

Remove:
  - RDMA handling from migration
  - dependencies on libibumad, libibverbs and librdmacm

Keep the RAM_SAVE_FLAG_HOOK definition since it might appears
in old migration streams.

Cc: Peter Xu <peterx@redhat.com>
Cc: Li Zhijian <lizhijian@fujitsu.com>
Acked-by: Fabiano Rosas <farosas@suse.de>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>

Just to be clear, because people raised the point in the last version,
the first link in the deprecation commit links to a thread comprising
entirely of rdma migration patches. I don't see any ambiguity on whether
the deprecation was intended to include migration. There's even an ack
from Juan.

Yes I remember that's the plan.


So on the basis of not reverting the previous maintainer's decision, my
Ack stands here.

We also had pretty obvious bugs ([1], [2]) in the past that would have
been caught if we had any kind of testing for the feature, so I can't
even say this thing works currently.

@Peter Xu, @Li Zhijian, what are your thoughts on this?

Generally I definitely agree with such a removal sooner or later, as that's
how deprecation works, and even after Juan's left I'm not aware of any
other new RDMA users.  Personally, I'd slightly prefer postponing it one
more release which might help a bit of our downstream maintenance, however
I assume that's not a blocker either, as I think we can also manage it.

IMHO it's more important to know whether there are still users and whether
they would still like to see it around.

Since e9a54265f5 was not very clear about rdma migration code, should we maybe rather add a separate deprecation note for the migration part, and add a proper warning message to the migration code in case someone tries to use it there, and then only remove the rdma migration code after two more releases?

 Thomas





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