Fabiano Rosas <[email protected]> writes:
> Add a new migration capability 'fixed-ram'.
>
> The core of the feature is to ensure that each RAM page has a specific
> offset in the resulting migration stream. The reasons why we'd want
> such behavior are:
>
> - The resulting file will have a bounded size, since pages which are
> dirtied multiple times will always go to a fixed location in the
> file, rather than constantly being added to a sequential
> stream. This eliminates cases where a VM with, say, 1G of RAM can
> result in a migration file that's 10s of GBs, provided that the
> workload constantly redirties memory.
>
> - It paves the way to implement O_DIRECT-enabled save/restore of the
> migration stream as the pages are ensured to be written at aligned
> offsets.
>
> - It allows the usage of multifd so we can write RAM pages to the
> migration file in parallel.
>
> For now, enabling the capability has no effect. The next couple of
> patches implement the core functionality.
>
> Signed-off-by: Fabiano Rosas <[email protected]>
[...]
> diff --git a/qapi/migration.json b/qapi/migration.json
> index 5a565d9b8d..3fce5fe53e 100644
> --- a/qapi/migration.json
> +++ b/qapi/migration.json
> @@ -531,6 +531,10 @@
> # and can result in more stable read performance. Requires KVM
> # with accelerator property "dirty-ring-size" set. (Since 8.1)
> #
> +# @fixed-ram: Migrate using fixed offsets in the migration file for
> +# each RAM page. Requires a migration URI that supports seeking,
> +# such as a file. (since 9.0)
> +#
> # Features:
> #
> # @deprecated: Member @block is deprecated. Use blockdev-mirror with
> @@ -555,7 +559,7 @@
> { 'name': 'x-ignore-shared', 'features': [ 'unstable' ] },
> 'validate-uuid', 'background-snapshot',
> 'zero-copy-send', 'postcopy-preempt', 'switchover-ack',
> - 'dirty-limit'] }
> + 'dirty-limit', 'fixed-ram'] }
>
> ##
> # @MigrationCapabilityStatus:
Can we find a better name than @fixed-ram? @fixed-ram-offsets?
@use-seek?
Apart from that, QAPI schema
Acked-by: Markus Armbruster <[email protected]>
