memory hotplug: align memmap to page size

To free memmap easier, this patch aligns it to page size.  Bootmem allocater
may mix some objects in one pages.  It's not good for freeing memmap of memory
hot-remove.
Signed-off-by: NYasunori Goto <y-goto@jp.fujitsu.com>
Cc: Badari Pulavarty <pbadari@us.ibm.com>
Cc: Yinghai Lu <yhlu.kernel@gmail.com>
Cc: Yasunori Goto <y-goto@jp.fujitsu.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/sparse.c

@@ -273,8 +273,8 @@ struct page __init *sparse_mem_map_populate(unsigned long pnum, int nid)
 	if (map)
 		return map;
 
-	map = alloc_bootmem_node(NODE_DATA(nid),
-			sizeof(struct page) * PAGES_PER_SECTION);
+	map = alloc_bootmem_pages_node(NODE_DATA(nid),
+		       PAGE_ALIGN(sizeof(struct page) * PAGES_PER_SECTION));
 	return map;
 }
 #endif /* !CONFIG_SPARSEMEM_VMEMMAP */