balloon question

["Jan Beulich" <jbeulich@novell.com>]

Running with Xen option dom0_mem=6G and kernel option mem=8G, I would have expected that I would see the system with a
2G balloon right after boot. However, the balloon is empty. Briefly looking at this, it would seem to me that, with all
pages being reserved when the system starts and only the populated ones getting the reserved status cleared in
__free_pages_bootmem(), the condition to put pages into the balloon in balloon_init() is inverted.

Also, dying in xen_destroy_contiguous_region() (and similarly in the failure recovery code in
xen_create_contiguous_region()) if the space just unmapped can't be re-populated seems overly harsh (we're having a case
where this actually happens); wouldn't it make sense to make this fatal only when the page can't be replaced by a free
one (allocated inside the domain, with the page stolen for this then simply pushed into the balloon, similar to
balloon_alloc_empty_page_range() except without freeing the memory to Xen)?

Thanks for clarification,
Jan