Re: [Qemu-devel] [PATCH v10 6/7] migration/ram.c: add a function to disable the bulk stage

[Peter Xu <peterx@redhat.com>]

On Mon, Dec 03, 2018 at 10:18:30AM +0800, Wei Wang wrote:
> This patch adds a function to enable a precopy notifier callback outside
> the migration subsystem to disable the bulk stage flag. This is needed by
> the free page optimization offered by virtio-balloon.
> 
> Signed-off-by: Wei Wang <wei.w.wang@intel.com>
> CC: Dr. David Alan Gilbert <dgilbert@redhat.com>
> CC: Juan Quintela <quintela@redhat.com>
> CC: Michael S. Tsirkin <mst@redhat.com>
> CC: Peter Xu <peterx@redhat.com>
> ---
>  include/migration/misc.h | 1 +
>  migration/ram.c          | 9 +++++++++
>  2 files changed, 10 insertions(+)
> 
> diff --git a/include/migration/misc.h b/include/migration/misc.h
> index 15f8d00..47e7ff5 100644
> --- a/include/migration/misc.h
> +++ b/include/migration/misc.h
> @@ -37,6 +37,7 @@ void precopy_infrastructure_init(void);
>  void precopy_add_notifier(NotifierWithReturn *n);
>  void precopy_remove_notifier(NotifierWithReturn *n);
>  int precopy_notify(PrecopyNotifyReason reason, Error **errp);
> +void precopy_disable_bulk_stage(void);
>  
>  void ram_mig_init(void);
>  void qemu_guest_free_page_hint(void *addr, size_t len);
> diff --git a/migration/ram.c b/migration/ram.c
> index b90a3f2..739dc97 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -354,6 +354,15 @@ int precopy_notify(PrecopyNotifyReason reason, Error **errp)
>      return notifier_with_return_list_notify(&precopy_notifier_list, &pnd);
>  }
>  
> +void precopy_disable_bulk_stage(void)
> +{
> +    if (!ram_state) {
> +        return;
> +    }
> +
> +    ram_state->ram_bulk_stage = false;
> +}
> +

This one is a bit tricky.  E.g., I think it'll at least affect XBZRLE
and compression somehow.  Since we will have the on-off switch for
balloon free page hinting so the user can at least decide what
features to use, with that I don't see much issue with it so far. But
I'd also like to see how other people see this change.

Regards,

-- 
Peter Xu