ree_tunable_compat.diff

diff --git c/gc.c w/gc.c
index 861379b..2f4d596 100644
--- c/gc.c
+++ w/gc.c
@@ -86,11 +86,13 @@ void *alloca ();
 #endif
 #define HEAP_MIN_SLOTS 10000
 #define FREE_MIN  4096
+#define HEAP_SLOTS_GROWTH_FACTOR 1.8
 
 typedef struct {
     unsigned int initial_malloc_limit;
     unsigned int initial_heap_min_slots;
     unsigned int initial_free_min;
+    double initial_heap_slots_growth_factor;
 #if defined(ENABLE_VM_OBJSPACE) && ENABLE_VM_OBJSPACE
     int gc_stress;
 #endif
@@ -100,6 +102,7 @@ static ruby_gc_params_t initial_params = {
     GC_MALLOC_LIMIT,
     HEAP_MIN_SLOTS,
     FREE_MIN,
+    HEAP_SLOTS_GROWTH_FACTOR,
 #if defined(ENABLE_VM_OBJSPACE) && ENABLE_VM_OBJSPACE
     FALSE,
 #endif
@@ -444,6 +447,7 @@ int *ruby_initial_gc_stress_ptr = &rb_objspace.gc_stress;
 #define initial_malloc_limit	initial_params.initial_malloc_limit
 #define initial_heap_min_slots	initial_params.initial_heap_min_slots
 #define initial_free_min	initial_params.initial_free_min
+#define initial_heap_slots_growth_factor  initial_params.initial_heap_slots_growth_factor
 
 #define is_lazy_sweeping(objspace) ((objspace)->heap.sweep_slots != 0)
 
@@ -478,7 +482,7 @@ static void initial_expand_heap(rb_objspace_t *objspace);
 void
 rb_gc_set_params(void)
 {
-    char *malloc_limit_ptr, *heap_min_slots_ptr, *free_min_ptr;
+    char *malloc_limit_ptr, *heap_min_slots_ptr, *free_min_ptr, *heap_slots_growth_factor_ptr;
 
     if (rb_safe_level() > 0) return;
 
@@ -505,7 +509,8 @@ rb_gc_set_params(void)
 	}
     }
 
-    free_min_ptr = getenv("RUBY_FREE_MIN");
+    if (!(free_min_ptr = getenv("RUBY_FREE_MIN")))
+        free_min_ptr = getenv("RUBY_HEAP_FREE_MIN");
     if (free_min_ptr != NULL) {
 	int free_min_i = atoi(free_min_ptr);
 	if (RTEST(ruby_verbose))
@@ -514,6 +519,17 @@ rb_gc_set_params(void)
 	    initial_free_min = free_min_i;
 	}
     }
+
+    heap_slots_growth_factor_ptr = getenv("RUBY_HEAP_SLOTS_GROWTH_FACTOR");
+    if (heap_slots_growth_factor_ptr != NULL) {
+    double growth_factor_d = atof(heap_slots_growth_factor_ptr);
+    if (RTEST(ruby_verbose))
+        fprintf(stderr, "heap_slots_growth_factor=%g (%g)\n",
+            growth_factor_d, initial_heap_slots_growth_factor);
+    if (growth_factor_d > 0) {
+        initial_heap_slots_growth_factor = growth_factor_d;
+    }
+    }
 }
 
 #if defined(ENABLE_VM_OBJSPACE) && ENABLE_VM_OBJSPACE
@@ -1302,7 +1318,7 @@ initial_expand_heap(rb_objspace_t *objspace)
 static void
 set_heaps_increment(rb_objspace_t *objspace)
 {
-    size_t next_heaps_length = (size_t)(heaps_used * 1.8);
+    size_t next_heaps_length = (size_t)(heaps_used * initial_heap_slots_growth_factor);
 
     if (next_heaps_length == heaps_used) {
         next_heaps_length++;