It has no references outside memory_hotplug.c.

Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Yasunori Goto <y-goto@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/memory_hotplug.h

@@ -69,7 +69,6 @@ extern void online_page(struct page *page);
 /* VM interface that may be used by firmware interface */
 extern int online_pages(unsigned long, unsigned long);
 extern void __offline_isolated_pages(unsigned long, unsigned long);
-extern int offline_pages(unsigned long, unsigned long, unsigned long);
 
 /* reasonably generic interface to expand the physical pages in a zone  */
 extern int __add_pages(int nid, struct zone *zone, unsigned long start_pfn,

mm/memory_hotplug.c

@@ -751,7 +751,7 @@ check_pages_isolated(unsigned long start_pfn, unsigned long end_pfn)
 	return offlined;
 }
 
-int offline_pages(unsigned long start_pfn,
+static int offline_pages(unsigned long start_pfn,
 		  unsigned long end_pfn, unsigned long timeout)
 {
 	unsigned long pfn, nr_pages, expire;