Age code to allow reclaiming old unexecuted functions

src/mark-compact.cc

Index: src/mark-compact.cc
diff --git a/src/mark-compact.cc b/src/mark-compact.cc
index 7c03a49e8536a4ace1e0e4aaa73eddeb22031a08..ab73e6979dcd19c16ddcd8042016a743accd6864 100644
--- a/src/mark-compact.cc
+++ b/src/mark-compact.cc
@@ -62,6 +62,7 @@ MarkCompactCollector::MarkCompactCollector() :  // NOLINT
       sweep_precisely_(false),
       reduce_memory_footprint_(false),
       abort_incremental_marking_(false),
+      marking_parity_(ODD_MARKING_PARITY),
       compacting_(false),
       was_marked_incrementally_(false),
       tracer_(NULL),
@@ -398,6 +399,13 @@ void MarkCompactCollector::CollectGarbage() {
 
   Finish();
 
+  if (marking_parity_ == EVEN_MARKING_PARITY) {
+    marking_parity_ = ODD_MARKING_PARITY;
+  } else {
+    ASSERT(marking_parity_ == ODD_MARKING_PARITY);
+    marking_parity_ = EVEN_MARKING_PARITY;
+  }
+
   tracer_ = NULL;
 }
 
@@ -1193,32 +1201,13 @@ class MarkCompactMarkingVisitor
   inline static bool IsFlushable(Heap* heap, JSFunction* function) {
     SharedFunctionInfo* shared_info = function->unchecked_shared();
 
-    // Code is either on stack, in compilation cache or referenced
-    // by optimized version of function.
-    MarkBit code_mark = Marking::MarkBitFrom(function->code());
-    if (code_mark.Get()) {
-      if (!Marking::MarkBitFrom(shared_info).Get()) {
-        shared_info->set_code_age(0);
-      }
-      return false;
-    }
-
-    // We do not flush code for optimized functions.
-    if (function->code() != shared_info->code()) {
-      return false;
-    }
-
-    return IsFlushable(heap, shared_info);
+    // Old code gets flushed if its shared_info is also flushable
+    return function->code()->IsOld() && IsFlushable(heap, shared_info);

[Michael Starzinger, 2012/10/02 14:58:59]

See comment below.

[danno, 2012/10/25 10:07:23]

Done.

   }
 
   inline static bool IsFlushable(Heap* heap, SharedFunctionInfo* shared_info) {
-    // Code is either on stack, in compilation cache or referenced
-    // by optimized version of function.
-    MarkBit code_mark =
-        Marking::MarkBitFrom(shared_info->code());
-    if (code_mark.Get()) {
-      return false;
-    }
+    // Code that is not old is not flushable.
+    if (!shared_info->code()->IsOld()) return false;

[Michael Starzinger, 2012/10/02 14:58:59]

1) We shouldn't remove the check for the marking bit of the code, because it
makes sure that we don't throw away un-optimized code that is required for
bailout from optimized code.

2) Also I don't think it makes much sense to flush code that is strongly
reachable through other paths, that will rather lead to increased memory
consumption because we keep recompiling code without actually collecting it.

3) Also it might be better to move this check further to the bottom, because it
is more expensive than the others I guess. But I don't have a strong opinion
about this last point.

[danno, 2012/10/25 10:07:23]

Done.

 
     // The function must be compiled and have the source code available,
     // to be able to recompile it in case we need the function again.
@@ -1247,12 +1236,6 @@ class MarkCompactMarkingVisitor
       return false;
     }
 
-    // Age this shared function info.
-    if (shared_info->code_age() < kCodeAgeThreshold) {
-      shared_info->set_code_age(shared_info->code_age() + 1);
-      return false;
-    }
-
     return true;
   }
 
@@ -1412,8 +1395,8 @@ class MarkCompactMarkingVisitor
       Code* code = jsfunction->shared()->code();
       MarkBit code_mark = Marking::MarkBitFrom(code);
       collector->MarkObject(code, code_mark);
-
       if (jsfunction->code()->kind() == Code::OPTIMIZED_FUNCTION) {
+        code->MakeYoung();
         collector->MarkInlinedFunctionsCode(jsfunction->code());
       }
     }
@@ -2730,6 +2713,14 @@ class PointersUpdatingVisitor: public ObjectVisitor {
     rinfo->set_target_address(Code::cast(target)->instruction_start());
   }
 
+  void VisitCodeAgeSequence(RelocInfo* rinfo) {
+    ASSERT(RelocInfo::IsCodeAgeSequence(rinfo->rmode()));
+    Object* stub = rinfo->code_age_stub();
+    ASSERT(stub != NULL);
+    VisitPointer(&stub);
+    rinfo->set_code_age_stub(Code::cast(stub));
+  }
+
   void VisitDebugTarget(RelocInfo* rinfo) {
     ASSERT((RelocInfo::IsJSReturn(rinfo->rmode()) &&
             rinfo->IsPatchedReturnSequence()) ||