diff --git a/include/jemalloc/internal/base.h b/include/jemalloc/internal/base.h
new file mode 100644
index 00000000..dcac3b6a
--- /dev/null
+++ b/include/jemalloc/internal/base.h
@@ -0,0 +1,103 @@
+#ifndef JEMALLOC_INTERNAL_BASE_H
+#define JEMALLOC_INTERNAL_BASE_H
+
+#include "jemalloc/internal/edata.h"
+#include "jemalloc/internal/ehooks.h"
+#include "jemalloc/internal/mutex.h"
+
+enum metadata_thp_mode_e {
+	metadata_thp_disabled   = 0,
+	/*
+	 * Lazily enable hugepage for metadata. To avoid high RSS caused by THP
+	 * + low usage arena (i.e. THP becomes a significant percentage), the
+	 * "auto" option only starts using THP after a base allocator used up
+	 * the first THP region.  Starting from the second hugepage (in a single
+	 * arena), "auto" behaves the same as "always", i.e. madvise hugepage
+	 * right away.
+	 */
+	metadata_thp_auto       = 1,
+	metadata_thp_always     = 2,
+	metadata_thp_mode_limit = 3
+};
+typedef enum metadata_thp_mode_e metadata_thp_mode_t;
+
+#define METADATA_THP_DEFAULT metadata_thp_disabled
+extern metadata_thp_mode_t opt_metadata_thp;
+extern const char *metadata_thp_mode_names[];
+
+
+/* Embedded at the beginning of every block of base-managed virtual memory. */
+typedef struct base_block_s base_block_t;
+struct base_block_s {
+	/* Total size of block's virtual memory mapping. */
+	size_t size;
+
+	/* Next block in list of base's blocks. */
+	base_block_t *next;
+
+	/* Tracks unused trailing space. */
+	edata_t edata;
+};
+
+typedef struct base_s base_t;
+struct base_s {
+	/*
+	 * User-configurable extent hook functions.
+	 */
+	ehooks_t ehooks;
+
+	/* Protects base_alloc() and base_stats_get() operations. */
+	malloc_mutex_t mtx;
+
+	/* Using THP when true (metadata_thp auto mode). */
+	bool auto_thp_switched;
+	/*
+	 * Most recent size class in the series of increasingly large base
+	 * extents.  Logarithmic spacing between subsequent allocations ensures
+	 * that the total number of distinct mappings remains small.
+	 */
+	pszind_t pind_last;
+
+	/* Serial number generation state. */
+	size_t extent_sn_next;
+
+	/* Chain of all blocks associated with base. */
+	base_block_t *blocks;
+
+	/* Heap of extents that track unused trailing space within blocks. */
+	edata_heap_t avail[SC_NSIZES];
+
+	/* Stats, only maintained if config_stats. */
+	size_t allocated;
+	size_t resident;
+	size_t mapped;
+	/* Number of THP regions touched. */
+	size_t n_thp;
+};
+
+static inline unsigned
+base_ind_get(const base_t *base) {
+	return ehooks_ind_get(&base->ehooks);
+}
+
+static inline bool
+metadata_thp_enabled(void) {
+	return (opt_metadata_thp != metadata_thp_disabled);
+}
+
+base_t *b0get(void);
+base_t *base_new(tsdn_t *tsdn, unsigned ind, extent_hooks_t *extent_hooks);
+void base_delete(tsdn_t *tsdn, base_t *base);
+ehooks_t *base_ehooks_get(base_t *base);
+extent_hooks_t *base_extent_hooks_set(base_t *base,
+    extent_hooks_t *extent_hooks);
+void *base_alloc(tsdn_t *tsdn, base_t *base, size_t size, size_t alignment);
+edata_t *base_alloc_edata(tsdn_t *tsdn, base_t *base);
+void base_stats_get(tsdn_t *tsdn, base_t *base, size_t *allocated,
+    size_t *resident, size_t *mapped, size_t *n_thp);
+void base_prefork(tsdn_t *tsdn, base_t *base);
+void base_postfork_parent(tsdn_t *tsdn, base_t *base);
+void base_postfork_child(tsdn_t *tsdn, base_t *base);
+bool base_boot(tsdn_t *tsdn);
+
+#endif /* JEMALLOC_INTERNAL_BASE_H */
diff --git a/include/jemalloc/internal/base_externs.h b/include/jemalloc/internal/base_externs.h
deleted file mode 100644
index 2f241317..00000000
--- a/include/jemalloc/internal/base_externs.h
+++ /dev/null
@@ -1,22 +0,0 @@
-#ifndef JEMALLOC_INTERNAL_BASE_EXTERNS_H
-#define JEMALLOC_INTERNAL_BASE_EXTERNS_H
-
-extern metadata_thp_mode_t opt_metadata_thp;
-extern const char *metadata_thp_mode_names[];
-
-base_t *b0get(void);
-base_t *base_new(tsdn_t *tsdn, unsigned ind, extent_hooks_t *extent_hooks);
-void base_delete(tsdn_t *tsdn, base_t *base);
-ehooks_t *base_ehooks_get(base_t *base);
-extent_hooks_t *base_extent_hooks_set(base_t *base,
-    extent_hooks_t *extent_hooks);
-void *base_alloc(tsdn_t *tsdn, base_t *base, size_t size, size_t alignment);
-edata_t *base_alloc_edata(tsdn_t *tsdn, base_t *base);
-void base_stats_get(tsdn_t *tsdn, base_t *base, size_t *allocated,
-    size_t *resident, size_t *mapped, size_t *n_thp);
-void base_prefork(tsdn_t *tsdn, base_t *base);
-void base_postfork_parent(tsdn_t *tsdn, base_t *base);
-void base_postfork_child(tsdn_t *tsdn, base_t *base);
-bool base_boot(tsdn_t *tsdn);
-
-#endif /* JEMALLOC_INTERNAL_BASE_EXTERNS_H */
diff --git a/include/jemalloc/internal/base_inlines.h b/include/jemalloc/internal/base_inlines.h
deleted file mode 100644
index 221fca81..00000000
--- a/include/jemalloc/internal/base_inlines.h
+++ /dev/null
@@ -1,13 +0,0 @@
-#ifndef JEMALLOC_INTERNAL_BASE_INLINES_H
-#define JEMALLOC_INTERNAL_BASE_INLINES_H
-
-static inline unsigned
-base_ind_get(const base_t *base) {
-	return ehooks_ind_get(&base->ehooks);
-}
-
-static inline bool
-metadata_thp_enabled(void) {
-	return (opt_metadata_thp != metadata_thp_disabled);
-}
-#endif /* JEMALLOC_INTERNAL_BASE_INLINES_H */
diff --git a/include/jemalloc/internal/base_types.h b/include/jemalloc/internal/base_types.h
deleted file mode 100644
index b6db77df..00000000
--- a/include/jemalloc/internal/base_types.h
+++ /dev/null
@@ -1,33 +0,0 @@
-#ifndef JEMALLOC_INTERNAL_BASE_TYPES_H
-#define JEMALLOC_INTERNAL_BASE_TYPES_H
-
-typedef struct base_block_s base_block_t;
-typedef struct base_s base_t;
-
-#define METADATA_THP_DEFAULT metadata_thp_disabled
-
-/*
- * In auto mode, arenas switch to huge pages for the base allocator on the
- * second base block.  a0 switches to thp on the 5th block (after 20 megabytes
- * of metadata), since more metadata (e.g. rtree nodes) come from a0's base.
- */
-
-#define BASE_AUTO_THP_THRESHOLD    2
-#define BASE_AUTO_THP_THRESHOLD_A0 5
-
-typedef enum {
-	metadata_thp_disabled   = 0,
-	/*
-	 * Lazily enable hugepage for metadata. To avoid high RSS caused by THP
-	 * + low usage arena (i.e. THP becomes a significant percentage), the
-	 * "auto" option only starts using THP after a base allocator used up
-	 * the first THP region.  Starting from the second hugepage (in a single
-	 * arena), "auto" behaves the same as "always", i.e. madvise hugepage
-	 * right away.
-	 */
-	metadata_thp_auto       = 1,
-	metadata_thp_always     = 2,
-	metadata_thp_mode_limit = 3
-} metadata_thp_mode_t;
-
-#endif /* JEMALLOC_INTERNAL_BASE_TYPES_H */
diff --git a/include/jemalloc/internal/edata_cache.h b/include/jemalloc/internal/edata_cache.h
index 9cb0d1c8..73ac7af8 100644
--- a/include/jemalloc/internal/edata_cache.h
+++ b/include/jemalloc/internal/edata_cache.h
@@ -1,6 +1,8 @@
 #ifndef JEMALLOC_INTERNAL_EDATA_CACHE_H
 #define JEMALLOC_INTERNAL_EDATA_CACHE_H
 
+#include "jemalloc/internal/base.h"
+
 /*
  * A cache of edata_t structures allocated via base_alloc_edata (as opposed to
  * the underlying extents they describe).  The contents of returned edata_t
diff --git a/include/jemalloc/internal/jemalloc_internal_includes.h b/include/jemalloc/internal/jemalloc_internal_includes.h
index 75a94d3a..72b5a72a 100644
--- a/include/jemalloc/internal/jemalloc_internal_includes.h
+++ b/include/jemalloc/internal/jemalloc_internal_includes.h
@@ -40,7 +40,6 @@
 /* TYPES */
 /******************************************************************************/
 
-#include "jemalloc/internal/base_types.h"
 #include "jemalloc/internal/arena_types.h"
 #include "jemalloc/internal/tcache_types.h"
 #include "jemalloc/internal/prof_types.h"
@@ -51,7 +50,6 @@
 
 #include "jemalloc/internal/prof_structs.h"
 #include "jemalloc/internal/arena_structs.h"
-#include "jemalloc/internal/base_structs.h"
 #include "jemalloc/internal/tcache_structs.h"
 #include "jemalloc/internal/background_thread_structs.h"
 
@@ -60,7 +58,6 @@
 /******************************************************************************/
 
 #include "jemalloc/internal/jemalloc_internal_externs.h"
-#include "jemalloc/internal/base_externs.h"
 #include "jemalloc/internal/arena_externs.h"
 #include "jemalloc/internal/large_externs.h"
 #include "jemalloc/internal/tcache_externs.h"
@@ -72,7 +69,6 @@
 /******************************************************************************/
 
 #include "jemalloc/internal/jemalloc_internal_inlines_a.h"
-#include "jemalloc/internal/base_inlines.h"
 /*
  * Include portions of arena code interleaved with tcache code in order to
  * resolve circular dependencies.
diff --git a/src/base.c b/src/base.c
index c006774e..595b7710 100644
--- a/src/base.c
+++ b/src/base.c
@@ -7,6 +7,15 @@
 #include "jemalloc/internal/mutex.h"
 #include "jemalloc/internal/sz.h"
 
+/*
+ * In auto mode, arenas switch to huge pages for the base allocator on the
+ * second base block.  a0 switches to thp on the 5th block (after 20 megabytes
+ * of metadata), since more metadata (e.g. rtree nodes) come from a0's base.
+ */
+
+#define BASE_AUTO_THP_THRESHOLD    2
+#define BASE_AUTO_THP_THRESHOLD_A0 5
+
 /******************************************************************************/
 /* Data. */