Xen balloon: fix totalram_pages counting.

Change totalram_pages when a single page is added/removed to the
ballooned list. This avoid totalram_pages to be set erroneously to
max_pfn at boot.

Signed-off-by: Gianluca Guida <[e-mail]>
Signed-off-by: Jeremy Fitzhardinge <[e-mail]>
Cc: Stable Kernel <[e-mail]>

drivers/xen/balloon.c

···
 		list_add(&page->lru, &ballooned_pages);
 		balloon_stats.balloon_low++;
 	}
+
+	totalram_pages--;
 }
 
 /* balloon_retrieve: rescue a page from the balloon, if it is not empty. */
···
 	}
 	else
 		balloon_stats.balloon_low--;
+
+	totalram_pages++;
 
 	return page;
 }
···
 	}
 
 	balloon_stats.current_pages += nr_pages;
-	totalram_pages = balloon_stats.current_pages;
 
  out:
 	spin_unlock_irqrestore(&balloon_lock, flags);
···
 	BUG_ON(ret != nr_pages);
 
 	balloon_stats.current_pages -= nr_pages;
-	totalram_pages = balloon_stats.current_pages;
 
 	spin_unlock_irqrestore(&balloon_lock, flags);
 
···
 	pr_info("xen_balloon: Initialising balloon driver.\n");
 
 	balloon_stats.current_pages = min(xen_start_info->nr_pages, max_pfn);
-	totalram_pages   = balloon_stats.current_pages;
 	balloon_stats.target_pages  = balloon_stats.current_pages;
 	balloon_stats.balloon_low   = 0;
 	balloon_stats.balloon_high  = 0;