Disconnects code objects from infrequently used unoptimized functions.

runtime/vm/pages.h

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_PAGES_H_
 #define VM_PAGES_H_
 
 #include "vm/freelist.h"
 #include "vm/globals.h"
 #include "vm/virtual_memory.h"
 
 namespace dart {
 
+DECLARE_FLAG(bool, collect_code);
+DECLARE_FLAG(bool, log_code_drop);
+
 // Forward declarations.
 class Heap;
 class ObjectPointerVisitor;
 
 // An aligned page containing old generation objects. Alignment is used to be
 // able to get to a HeapPage header quickly based on a pointer to an object.
 class HeapPage {
  public:
   enum PageType {
     kData = 0,
@@ skipping 90 matching lines @@
 
   bool CanGrowPageSpace(intptr_t size_in_bytes);
 
   // A garbage collection is considered as successful if more than
   // heap_growth_ratio % of memory got deallocated by the garbage collector.
   // In this case garbage collection will be performed next time. Otherwise
   // the heap will grow.
   void EvaluateGarbageCollection(intptr_t in_use_before, intptr_t in_use_after,
                                  int64_t start, int64_t end);
 
+  int64_t last_code_collection_in_us() { return last_code_collection_in_us_; }
+  void set_last_code_collection_in_us(int64_t t) {
+    last_code_collection_in_us_ = t;
+  }
+
   void set_is_enabled(bool state) {
     is_enabled_ = state;
   }
   bool is_enabled() {
     return is_enabled_;
   }
 
  private:
   bool is_enabled_;
 
   // Heap growth control variable.
   intptr_t grow_heap_;
 
   // If the garbage collector was not able to free more than heap_growth_ratio_
   // memory, then the heap is grown. Otherwise garbage collection is performed.
   int heap_growth_ratio_;
 
   // The desired percent of heap in-use after a garbage collection.
   // Equivalent to \frac{100-heap_growth_ratio_}{100}.
   double desired_utilization_;
 
   // Number of pages we grow.
   int heap_growth_rate_;
 
   // If the relative GC time stays below garbage_collection_time_ratio_
   // garbage collection can be performed.
   int garbage_collection_time_ratio_;
 
+  // The time in microseconds of the last time we tried to collect unused
+  // code.
+  int64_t last_code_collection_in_us_;
+
   PageSpaceGarbageCollectionHistory history_;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(PageSpaceController);
 };
 
 
 class PageSpace {
  public:
   // TODO(iposva): Determine heap sizes and tune the page size accordingly.
   static const intptr_t kPageSize = 256 * KB;
@@ skipping 19 matching lines @@
   bool IsValidAddress(uword addr) const {
     return Contains(addr);
   }
 
   void VisitObjects(ObjectVisitor* visitor) const;
   void VisitObjectPointers(ObjectPointerVisitor* visitor) const;
 
   RawObject* FindObject(FindObjectVisitor* visitor,
                         HeapPage::PageType type) const;
 
+  // Runs a visitor that attempts to drop references to code that has not
+  // been run in awhile.
+  void TryDetachingCode();
+
   // Collect the garbage in the page space using mark-sweep.
   void MarkSweep(bool invoke_api_callbacks);
 
   void StartEndAddress(uword* start, uword* end) const;
 
   void SetGrowthControlState(bool state) {
     page_space_controller_.set_is_enabled(state);
   }
 
   bool GrowthControlState() {
@@ skipping 51 matching lines @@
   PageSpaceController page_space_controller_;
 
   friend class PageSpaceController;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(PageSpace);
 };
 
 }  // namespace dart
 
 #endif  // VM_PAGES_H_