2 files changed, 17 insertions, 1 deletions
diff --git a/src/gc.c b/src/gc.c
index 472535925..b3e4b291c 100644
--- a/src/gc.c
+++ b/src/gc.c
@@ -147,8 +147,10 @@ gettimeofday_time(void)
 #ifdef GC_DEBUG
 #include <assert.h>
 #define gc_assert(expect) assert(expect)
+#define DEBUG(x) (x)
 #else
 #define gc_assert(expect) ((void)0)
+#define DEBUG(x)
 #endif
 
 #define GC_STEP_SIZE 1024
@@ -206,6 +208,7 @@ struct heap_page {
   struct heap_page *next;
   struct heap_page *free_next;
   struct heap_page *free_prev;
+  unsigned int old:1;
   RVALUE objects[MRB_HEAP_PAGE_SIZE];
 };
 
@@ -762,6 +765,11 @@ incremental_sweep_phase(mrb_state *mrb, size_t limit)
     int dead_slot = 1;
     int full = (page->freelist == NULL);
 
+    if (is_minor_gc(mrb) && page->old) {
+      /* skip a slot which doesn't contain any young object */
+      p = e;
+      dead_slot = 0;
+    }
     while (p<e) {
       if (is_dead(mrb, &p->as.basic)) {
         if (p->as.basic.tt != MRB_TT_FREE) {
@@ -792,6 +800,10 @@ incremental_sweep_phase(mrb_state *mrb, size_t limit)
       if (full && freed > 0) {
         link_free_heap_page(mrb, page);
       }
+      if (page->freelist == NULL && is_minor_gc(mrb))
+        page->old = TRUE;
+      else
+        page->old = FALSE;
       page = page->next;
     }
     tried_sweep += MRB_HEAP_PAGE_SIZE;
diff --git a/src/vm.c b/src/vm.c
index b84158d1d..8ae28ef5e 100644
--- a/src/vm.c
+++ b/src/vm.c
@@ -49,7 +49,11 @@ The value below allows about 60000 recursive calls in the simplest case. */
 #define MRB_STACK_MAX ((1<<18) - MRB_STACK_GROWTH)
 #endif
 
-
+#ifdef VM_DEBUG
+# define DEBUG(x) (x)
+#else
+# define DEBUG(x)
+#endif
 
 static inline void
 stack_copy(mrb_value *dst, const mrb_value *src, size_t size)