Re: [PATCH v4 6/7] migration/multifd: Add zero pages and zero bytes counter to migration status interface.

[Markus Armbruster]

Hao Xiang <hao.xiang@bytedance.com> writes:

> This change extends the MigrationStatus interface to track zero pages
> and zero bytes counter.
>
> Signed-off-by: Hao Xiang <hao.xiang@bytedance.com>

[...]

> diff --git a/qapi/migration.json b/qapi/migration.json
> index ca9561fbf1..03b850bab7 100644
> --- a/qapi/migration.json
> +++ b/qapi/migration.json
> @@ -63,6 +63,10 @@
>  #     between 0 and @dirty-sync-count * @multifd-channels.  (since
>  #     7.1)
>  #
> +# @zero-pages: number of zero pages (since 9.0)
> +#
> +# @zero-bytes: number of zero bytes sent (since 9.0)
> +#

Discussion of v3 has led me to believe:

1. A page is either migrated as a normal page or as a zero page.

2. The following equations hold:

    @normal-bytes = @normal * @page-size

    @zero-bytes = @zero-pages * @page-size

3. @zero-pages is the same as @duplicate, with a better name.  We intend
   to drop @duplicate eventually.

If this is correct, I'd like you to

A. Name it @zero for consistency with @normal.  Disregard my advice to
   name it @zero-pages; two consistent bad names are better than one bad
   name, one good name, and inconsistency.

B. Add @zero and @zero-bytes next to @normal and @normal-bytes.

C. Deprecate @duplicate (item 3).  Separate patch, please.

D. Consider documenting more clearly what normal and zero pages are
   (item 1), and how @FOO, @FOO-pages and @page-size are related (item
   2).  Could be done in a followup patch.

>  # Features:
>  #
>  # @deprecated: Member @skipped is always zero since 1.5.3
> @@ -81,7 +85,8 @@
>             'multifd-bytes': 'uint64', 'pages-per-second': 'uint64',
>             'precopy-bytes': 'uint64', 'downtime-bytes': 'uint64',
>             'postcopy-bytes': 'uint64',
> -           'dirty-sync-missed-zero-copy': 'uint64' } }
> +           'dirty-sync-missed-zero-copy': 'uint64',
> +           'zero-pages': 'int', 'zero-bytes': 'size' } }
>  

[...]