Index: gc.c
===================================================================
--- gc.c	(revision 25630)
+++ gc.c	(working copy)
@@ -296,6 +296,7 @@
     struct {
 	size_t limit;
 	size_t increase;
+	size_t count;
 #if CALC_EXACT_MALLOC_SIZE
 	size_t allocated_size;
 	size_t allocations;
@@ -345,6 +346,7 @@
 #endif
 #define malloc_limit		objspace->malloc_params.limit
 #define malloc_increase 	objspace->malloc_params.increase
+#define malloc_count		objspace->malloc_params.count
 #define heap_slots		objspace->heap.slots
 #define heaps			objspace->heap.ptr
 #define heaps_length		objspace->heap.length
@@ -664,6 +666,7 @@
 	}
     }
     malloc_increase += size;
+    malloc_count++;
 
 #if CALC_EXACT_MALLOC_SIZE
     objspace->malloc_params.allocated_size += size;
@@ -679,6 +682,7 @@
 vm_xrealloc(rb_objspace_t *objspace, void *ptr, size_t size)
 {
     void *mem;
+    int increase_size;
 
     if ((ssize_t)size < 0) {
 	negative_size_allocation_error("negative re-allocation size");
@@ -688,8 +692,16 @@
 	vm_xfree(objspace, ptr);
 	return 0;
     }
-    if (ruby_gc_stress && !ruby_disable_gc_stress)
+
+    increase_size = size - malloc_increase / (malloc_count + 1);
+    if (increase_size < 0) {
+	increase_size = 0;
+    }
+    
+    if ((ruby_gc_stress && !ruby_disable_gc_stress) ||
+	(malloc_increase+increase_size) > malloc_limit) {
 	garbage_collect_with_gvl(objspace);
+    }
 
 #if CALC_EXACT_MALLOC_SIZE
     size += sizeof(size_t);
@@ -706,7 +718,7 @@
 	    ruby_memerror();
         }
     }
-    malloc_increase += size;
+    malloc_increase += increase_size;
 
 #if CALC_EXACT_MALLOC_SIZE
     objspace->malloc_params.allocated_size += size;
@@ -1921,6 +1933,7 @@
 	if (malloc_limit < GC_MALLOC_LIMIT) malloc_limit = GC_MALLOC_LIMIT;
     }
     malloc_increase = 0;
+    malloc_count = 0;
     if (freed < free_min) {
         set_heaps_increment(objspace);
         heaps_increment(objspace);