* gc.c (gc_writebarrier_generational): add an alternative write

barrier (WB) implementation.
  When finding reference from [Old obj] to [New obj] by WB, current
  implementation marks [Old obj] as remembered old objects and marks
  chilldren of [Old obj] at the beggining of marking.
  Added (but disabled) code changes current behaviour. This fix promote
  [New obj] to old and marks as a remembered old object. We can assume
  "new objects referred from old objects are maybe long-lived old
  objects".
  Disadvantage of added algorithm is we may promote unwilling
  short-lived objects. For example, consider many new objects push and
  pop to an old stack object. All of new objects (short-lived objects)
  promote to old objects unexpectedly.
  To compare these behaviour, I add this new code (but disabled it).



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@50006 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,3 +1,23 @@
+Wed Mar 18 17:21:12 2015  Koichi Sasada  <ko1@atdot.net>
+
+	* gc.c (gc_writebarrier_generational): add an alternative write
+	  barrier (WB) implementation.
+	  When finding reference from [Old obj] to [New obj] by WB, current
+	  implementation marks [Old obj] as remembered old objects and marks
+	  chilldren of [Old obj] at the beggining of marking.
+
+	  Added (but disabled) code changes current behaviour. This fix promote
+	  [New obj] to old and marks as a remembered old object. We can assume
+	  "new objects referred from old objects are maybe long-lived old
+	  objects".
+
+	  Disadvantage of added algorithm is we may promote unwilling 
+	  short-lived objects. For example, consider many new objects push and
+	  pop to an old stack object. All of new objects (short-lived objects)
+	  promote to old objects unexpectedly.
+
+	  To compare these behaviour, I add this new code (but disabled it).
+
 Wed Mar 18 17:14:39 2015  Koichi Sasada  <ko1@atdot.net>
 
 	* gc.c (RVALUE_PROMOTE_RAW): rename to RVALUE_OLD_LONG_LIVED_SET()

gc.c

@@ -5464,15 +5464,33 @@ static void
 gc_writebarrier_generational(rb_objspace_t *objspace, VALUE a, VALUE b)
 {
     if (RGENGC_CHECK_MODE) {
-	if (!RVALUE_OLD_P(a)) rb_bug("rb_gc_writebarrier_generational: %s is not an old object.", obj_info(a));
-	if ( RVALUE_OLD_P(b)) rb_bug("rb_gc_writebarrier_generational: %s is an old object.", obj_info(b));
+	if (!RVALUE_OLD_P(a)) rb_bug("gc_writebarrier_generational: %s is not an old object.", obj_info(a));
+	if ( RVALUE_OLD_P(b)) rb_bug("gc_writebarrier_generational: %s is an old object.", obj_info(b));
 	if (is_incremental_marking(objspace)) rb_bug("rb_gc_writebarrier_generational: called while incremental marking: %s -> %s", obj_info(a), obj_info(b));
     }
 
+#if 1
+    /* mark `a' and remember (default behaviour) */
     if (!rgengc_remembered(objspace, a)) {
-	gc_report(1, objspace, "rb_gc_writebarrier_generational: %s -> %s\n", obj_info(a), obj_info(b));
 	rgengc_remember(objspace, a);
+	gc_report(1, objspace, "rb_gc_writebarrier_generational: %s (remembered) -> %s\n", obj_info(a), obj_info(b));
     }
+#else
+    /* mark `b' and remember */
+    MARK_IN_BITMAP(GET_HEAP_MARK_BITS(b), b);
+    if (RVALUE_WB_UNPROTECTED(b)) {
+	gc_remember_unprotected(objspace, b);
+    }
+    else {
+	RVALUE_AGE_SET_OLD(objspace, b);
+	rgengc_remember(objspace, b);
+    }
+
+    gc_report(1, objspace, "gc_writebarrier_generational: %s -> %s (remembered)\n", obj_info(a), obj_info(b));
+#endif
+
+    check_rvalue_consistency(a);
+    check_rvalue_consistency(b);
 }
 
 #if GC_ENABLE_INCREMENTAL_MARK