Re: [PATCH 02/10] migration/rdma: Remove unregister code

[Yanfei Xu <isyanfei.xu@gmail.com>]

Hi Peter,

No objection to removing the dead code — it clearly never worked

I do have one question about the direction, though. The removed logic
was the only in-tree attempt at MR unregistration for the non-pin-all
path. Without it, registered MRs grow monotonically over a migration,
and with large, widely-spread dirty memory over chunks the accumulated
MR metadata (user + kernel) can cost more than pin-all and even perform
worse — which rather defeats the purpose of not pinning everything.

do we still intend to keep and improve the non-pin-all path going
forward? If so, some form of dynamic MR unregistration will eventually
be needed and it might be worth keeping this code，or at least leaving
a TODO to mark the gap?

Thanks,
Yanfei

On 2026/8/18 04:24, Peter Xu wrote:
> The unregister code was there since the first commit RDMA migration was
> merged, but it was never functioning.  Remove the dead code.
>
> Since the two control messages are the last ones, we don't even need to
> worry about compatibility of legacy RDMA control commands, we can directly
> remove the messages too.
>
> As a side effect, this patch closes a report by removing the code
> completely.
>
> Reported-by: Tristan (@TristanInSec)
> Closes:https://gitlab.com/qemu-project/qemu/-/work_items/4003
> Signed-off-by: Peter Xu<peterx@redhat.com>