David Hildenbrand <da...@redhat.com> wrote:
> To achieve desired "x-ignore-shared" functionality, we should not
> discard all RAM when realizing the device and not mess with
> preallocation/postcopy when loading device state. In essence, we should
> not touch RAM content.
>
> As "x-ignore-shared" gets set after realizing the device, we cannot
> rely on that. Let's simply skip discarding of RAM on incoming migration.
> Note that virtio_mem_post_load() will call
> virtio_mem_restore_unplugged() -- unless "x-ignore-shared" is set. So
> once migration finished we'll have a consistent state.
>
> The initial system reset will also not discard any RAM, because
> virtio_mem_unplug_all() will not call virtio_mem_unplug_all() when no
> memory is plugged (which is the case before loading the device state).
>
> Note that something like VM templating -- see commit b17fbbe55cba
> ("migration: allow private destination ram with x-ignore-shared") -- is
> currently incompatible with virtio-mem and ram_block_discard_range() will
> warn in case a private file mapping is supplied by virtio-mem.
>
> For VM templating with virtio-mem, it makes more sense to either
> (a) Create the template without the virtio-mem device and hotplug a
> virtio-mem device to the new VM instances using proper own memory
> backend.
> (b) Use a virtio-mem device that doesn't provide any memory in the
> template (requested-size=0) and use private anonymous memory.
>
> Tested-by: Mario Casquero <mcasq...@redhat.com>
> Signed-off-by: David Hildenbrand <da...@redhat.com>
After very nice explanation.
Reviewed-by: Juan Quintela <quint...@redhat.com>
