ko1	2015-03-18 18:02:10 +0900 (Wed, 18 Mar 2015)

  New Revision: 50006

  http://svn.ruby-lang.org/cgi-bin/viewvc.cgi?view=revision&revision=50006

  Log:
    * 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).

  Modified files:
    trunk/ChangeLog
    trunk/gc.c
Index: ChangeLog
===================================================================
--- ChangeLog	(revision 50005)
+++ ChangeLog	(revision 50006)
@@ -1,3 +1,23 @@ https://github.com/ruby/ruby/blob/trunk/ChangeLog#L1
+Wed Mar 18 17:21:12 2015  Koichi Sasada  <ko1@a...>
+
+	* 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@a...>
 
 	* gc.c (RVALUE_PROMOTE_RAW): rename to RVALUE_OLD_LONG_LIVED_SET()
Index: gc.c
===================================================================
--- gc.c	(revision 50005)
+++ gc.c	(revision 50006)
@@ -5464,15 +5464,33 @@ static void https://github.com/ruby/ruby/blob/trunk/gc.c#L5464
 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

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