diff --git a/gc.c b/gc.c
index 8c718aca..a092f387 100644
--- a/gc.c
+++ b/gc.c
@@ -1648,11 +1648,29 @@ void gc_thread_data_init(gc_thread_data * thd, int mut_num, char *stack_base,
     fprintf(stderr, "Unable to initialize thread mutex\n");
     exit(1);
   }
+  thd->heap = calloc(1, sizeof(gc_heap_root));
+  thd->heap->heap = calloc(1, sizeof(gc_heap *) * NUM_HEAP_TYPES);
+  thd->heap->heap[HEAP_REST] = gc_heap_create(HEAP_REST, INITIAL_HEAP_SIZE, 0, 0);
+  thd->heap->heap[HEAP_SM] = gc_heap_create(HEAP_SM, INITIAL_HEAP_SIZE, 0, 0);
+  thd->heap->heap[HEAP_64] = gc_heap_create(HEAP_64, INITIAL_HEAP_SIZE, 0, 0);
+  if (sizeof(void *) == 8) { // Only use this heap on 64-bit platforms
+    thd->heap[HEAP_96] = gc_heap_create(HEAP_96, INITIAL_HEAP_SIZE, 0, 0);
+  }
+  thd->heap->heap[HEAP_HUGE] = gc_heap_create(HEAP_HUGE, 1024, 0, 0);
+  thd->cached_heap_free_sizes = calloc(5, sizeof(uint64_t));
+  thd->cached_heap_total_sizes = calloc(5, sizeof(uint64_t));
 }
 
 void gc_thread_data_free(gc_thread_data * thd)
 {
   if (thd) {
+//
+// !!
+// TODO: (not necessarily here, but somewhere need to roll heap pages into
+// another thread data. need to include cached heap sizes/total, too.
+// then free cached heap vars here.
+// !!
+//
     if (pthread_mutex_destroy(&thd->lock) != 0) {
       // TODO: can only destroy the lock if it is unlocked. need to make sure we
       // can guarantee that is the case prior to making this call
diff --git a/include/cyclone/types.h b/include/cyclone/types.h
index 2c586a2b..af6e6090 100644
--- a/include/cyclone/types.h
+++ b/include/cyclone/types.h
@@ -17,6 +17,7 @@
 #include <string.h>
 #include <time.h>
 #include <pthread.h>
+#include <stdint.h>
 
 // Maximum number of args that GC will accept
 #define NUM_GC_ARGS 128
@@ -141,6 +142,9 @@ struct gc_thread_data_t {
   int mark_buffer_len;
   pthread_mutex_t lock;
   pthread_t thread_id;
+  gc_heap_root *heap;
+  uint64_t *cached_heap_free_sizes;
+  uint64_t *cached_heap_total_sizes;
   // Data needed for call history
   char **stack_traces;
   int stack_trace_idx;
diff --git a/runtime.c b/runtime.c
index 76e6f8bd..55d15ad4 100644
--- a/runtime.c
+++ b/runtime.c
@@ -140,7 +140,6 @@ if (type_is_pair_prim(clo)) { \
 /*END closcall section */
 
 /* Global variables. */
-static gc_heap_root *Cyc_heap;
 object Cyc_global_variables = NULL;
 int _cyc_argc = 0;
 char **_cyc_argv = NULL;
@@ -261,17 +260,6 @@ static bool set_insert(ck_hs_t * hs, const void *value)
 
 void gc_init_heap(long heap_size)
 {
-  size_t initial_heap_size = INITIAL_HEAP_SIZE;
-  Cyc_heap = calloc(1, sizeof(gc_heap_root));
-  Cyc_heap->heap = calloc(1, sizeof(gc_heap *) * NUM_HEAP_TYPES);
-  Cyc_heap->heap[HEAP_REST] = gc_heap_create(HEAP_REST, initial_heap_size, 0, 0);
-  Cyc_heap->heap[HEAP_SM] = gc_heap_create(HEAP_SM, initial_heap_size, 0, 0);
-  Cyc_heap->heap[HEAP_64] = gc_heap_create(HEAP_64, initial_heap_size, 0, 0);
-  if (sizeof(void *) == 8) { // Only use this heap on 64-bit platforms
-    Cyc_heap->heap[HEAP_96] = gc_heap_create(HEAP_96, initial_heap_size, 0, 0);
-  }
-  Cyc_heap->heap[HEAP_HUGE] = gc_heap_create(HEAP_HUGE, 1024, 0, 0);
-
   if (!ck_hs_init(&symbol_table,
                   CK_HS_MODE_OBJECT | CK_HS_MODE_SPMC,
                   hs_hash, hs_compare,