failed_addition:
+#ifdef CONFIG_DEBUG_VM
 	pr_debug("online_pages [mem %#010llx-%#010llx] failed\n",
 		 (unsigned long long) pfn << PAGE_SHIFT,
 		 (((unsigned long long) pfn + nr_pages) << PAGE_SHIFT) - 1);
+#endif

I have never been sure about this.
IMO, if I fail to online pages, I want to know I failed.
I think that pr_err would be better than pr_debug and without CONFIG_DEBUG_VM.

But at least, if not, envolve it with a CONFIG_DEBUG_VM, but change pr_debug to pr_info.

+#ifdef CONFIG_DEBUG_VM
 	pr_debug("memory offlining [mem %#010llx-%#010llx] failed\n",
 		 (unsigned long long) start_pfn << PAGE_SHIFT,
 		 ((unsigned long long) end_pfn << PAGE_SHIFT) - 1);
+#endif

Same goes here.

Thanks
-- 
Oscar Salvador
SUSE L3