When CONFIG_XEN_BALLOON_MEMORY_HOTPLUG is not defined
reserve_additional_memory() will set balloon_stats.target_pages to a
wrong value in case there are still some ballooned pages allocated via
alloc_xenballooned_pages().
This will result in balloon_process() no longer be triggered when
ballooned pages are freed in batches.
Reported-by: Nicholas Tsirakis <niko.tsirakis@xxxxxxxxx>
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>