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..2cd79bf4393ebb6930215e332b29a97bf6e9e1a1 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),

[Michael Starzinger, 2012/09/21 09:43:19]

The default should be NO_MARKING_PARITY I think.

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

Done.

       compacting_(false),
       was_marked_incrementally_(false),
       tracer_(NULL),
@@ -398,6 +399,13 @@ void MarkCompactCollector::CollectGarbage() {
 
   Finish();
 
+  if (marking_parity_ == EVEN_MARKING_PARITY) {

[Michael Starzinger, 2012/09/21 09:43:19]

I think it would be safer to set the marking parity in
MarkCompactCollector::Prepare before we start a cycle and then reset it back to
NO_MARKING_PARITY again in MarkCompactCollector::Finish. Thereby we will catch
misuse of the parity value somewhere outside a cycle, where it makes no sense.

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

Done.

+    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);
   }
 
   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;
 
     // 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 +2713,15 @@ 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();
+    if (stub != NULL) {

[Michael Starzinger, 2012/09/21 09:43:19]

Can the stub really be NULL here? Shouldn't we only visit the relocation info
when there actually is an aging stub call present?

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

Done.

+      VisitPointer(&stub);
+      rinfo->set_code_age_stub(Code::cast(stub));
+    }
+  }
+
   void VisitDebugTarget(RelocInfo* rinfo) {
     ASSERT((RelocInfo::IsJSReturn(rinfo->rmode()) &&
             rinfo->IsPatchedReturnSequence()) ||