+#ifdef CONFIG_SPARSEMEM_EXTREME
+static struct mem_section *sparse_index_alloc(int nid)
+{
+ struct mem_section *section = NULL;
+ unsigned long array_size = SECTIONS_PER_ROOT *
+ sizeof(struct mem_section);
+
+ section = alloc_bootmem_node(NODE_DATA(nid), array_size);
+
+ if (section)
+ memset(section, 0, array_size);
+
+ return section;
+}
+
+static int sparse_index_init(unsigned long section_nr, int nid)
+{
+ static spinlock_t index_init_lock = SPIN_LOCK_UNLOCKED;
+ unsigned long root = SECTION_NR_TO_ROOT(section_nr);
+ struct mem_section *section;
+ int ret = 0;
+
+ if (mem_section[root])
+ return -EEXIST;
+
+ section = sparse_index_alloc(nid);
+ /*
+ * This lock keeps two different sections from
+ * reallocating for the same index
+ */
+ spin_lock(&index_init_lock);
+
+ if (mem_section[root]) {
+ ret = -EEXIST;
+ goto out;
+ }
+
+ mem_section[root] = section;
+out:
+ spin_unlock(&index_init_lock);
+ return ret;
+}
+#else /* !SPARSEMEM_EXTREME */
+static inline int sparse_index_init(unsigned long section_nr, int nid)
+{
+ return 0;
+}
+#endif
+