Re: [PATCH 1/6] migration: remove RDMA live migration temporarily

[Markus Armbruster <armbru@redhat.com>]

Gonglei <arei.gonglei@huawei.com> writes:

> From: Jialin Wang <wangjialin23@huawei.com>
>
> The new RDMA live migration will be introduced in the upcoming
> few commits.
>
> Signed-off-by: Jialin Wang <wangjialin23@huawei.com>
> Signed-off-by: Gonglei <arei.gonglei@huawei.com>

[...]

> diff --git a/qapi/migration.json b/qapi/migration.json
> index a351fd3714..4d7d49bfec 100644
> --- a/qapi/migration.json
> +++ b/qapi/migration.json
> @@ -210,9 +210,9 @@
>  #
>  # @setup-time: amount of setup time in milliseconds *before* the
>  #     iterations begin but *after* the QMP command is issued.  This is
> -#     designed to provide an accounting of any activities (such as
> -#     RDMA pinning) which may be expensive, but do not actually occur
> -#     during the iterative migration rounds themselves.  (since 1.6)
> +#     designed to provide an accounting of any activities which may be
> +#     expensive, but do not actually occur during the iterative migration
> +#     rounds themselves.  (since 1.6)

I guess the new RDMA migration code will not do RDMA pinning.  Correct?

>  #
>  # @cpu-throttle-percentage: percentage of time guest cpus are being
>  #     throttled during auto-converge.  This is only present when
> @@ -378,10 +378,6 @@
>  #     for certain work loads, by sending compressed difference of the
>  #     pages
>  #
> -# @rdma-pin-all: Controls whether or not the entire VM memory
> -#     footprint is mlock()'d on demand or all at once.  Refer to
> -#     docs/rdma.txt for usage.  Disabled by default.  (since 2.0)
> -#
>  # @zero-blocks: During storage migration encode blocks of zeroes
>  #     efficiently.  This essentially saves 1MB of zeroes per block on
>  #     the wire.  Enabling requires source and target VM to support
> @@ -476,7 +472,7 @@
>  # Since: 1.2
>  ##
>  { 'enum': 'MigrationCapability',
> -  'data': ['xbzrle', 'rdma-pin-all', 'auto-converge', 'zero-blocks',
> +  'data': ['xbzrle', 'auto-converge', 'zero-blocks',
>             'events', 'postcopy-ram',
>             { 'name': 'x-colo', 'features': [ 'unstable' ] },
>             'release-ram',

I guess you remove @rdma-pin-all, because it makes no sense with the new
migration code.  However, this is an incompatible change.

Here's the orderly way to remove it:

1. Document it doesn't do anything anymore, and deprecate it.

2. Remove after the deprecation grace period (two releases, see
docs/about/deprecated.rst.

> @@ -533,7 +529,6 @@
>  #     -> { "execute": "query-migrate-capabilities" }
>  #     <- { "return": [
>  #           {"state": false, "capability": "xbzrle"},
> -#           {"state": false, "capability": "rdma-pin-all"},
>  #           {"state": false, "capability": "auto-converge"},
>  #           {"state": false, "capability": "zero-blocks"},
>  #           {"state": true, "capability": "events"},

[...]