Index: kernel/generic/include/lib/ra.h
===================================================================
--- kernel/generic/include/lib/ra.h	(revision 375fc3fddae54b55e346c160f38e921349923c0f)
+++ kernel/generic/include/lib/ra.h	(revision 961c0484519f4f59bbfc17feda26b91c8046c90a)
@@ -45,5 +45,5 @@
 
 typedef struct {
-	link_t span_link;	/**< Link for the arena's list of spans. */
+	link_t span_link;	/**< Arena's list of spans link. */
 
 	list_t segments;	/**< List of span's segments. */
@@ -53,18 +53,25 @@
 
 	hash_table_t used;
+
+	uintptr_t base;		/**< Span base. */
+	size_t size;		/**< Span size. */
 } ra_span_t;
 
+/*
+ * We would like to achieve a good ratio of the size of one unit of the
+ * represented resource (e.g. a page) and sizeof(ra_segment_t).  We therefore
+ * attempt to have as few redundant information in the segment as possible. For
+ * example, the size of the segment needs to be calculated from the segment
+ * base and the base of the following segment.
+ */
 typedef struct {
-	link_t segment_link;	/**< Link for the span's list of segments. */
-	link_t free_link;	/**< Link for the span's free list. */
-	link_t used_link;	/**< Link for the span's used hash table. */
+	link_t segment_link;	/**< Span's segment list link. */
+	link_t fu_link;		/**< Span's free list or used hash link. */
 
 	uintptr_t base;		/**< Segment base. */
-	uintptr_t size;		/**< Segment size. */
-	
 } ra_segment_t;
 
 extern ra_arena_t *ra_arena_create(uintptr_t, size_t);
-extern void ra_span_add(ra_arena_t *, uintptr_t, size_t);
+extern bool ra_span_add(ra_arena_t *, uintptr_t, size_t);
 extern uintptr_t ra_alloc(ra_arena_t *, size_t, size_t);
 extern void ra_free(ra_arena_t *, uintptr_t, size_t);