Add memory pressure notification API

src/heap/heap.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_HEAP_HEAP_H_
 #define V8_HEAP_HEAP_H_
 
 #include <cmath>
 #include <map>
 
@@ skipping 394 matching lines @@
 };
 
 
 enum ArrayStorageAllocationMode {
   DONT_INITIALIZE_ARRAY_ELEMENTS,
   INITIALIZE_ARRAY_ELEMENTS_WITH_HOLE
 };
 
 enum class ClearRecordedSlots { kYes, kNo };
 
+enum class MemoryPressureLevel { kNone, kModerate, kCritical };

[jochen (gone - plz use gerrit), 2016/03/17 19:33:39]

why not just use the external class?

[ulan, 2016/03/18 12:49:41]

Done.

+
 class Heap {
  public:
   // Declare all the root indices.  This defines the root list order.
   enum RootListIndex {
 #define ROOT_INDEX_DECLARATION(type, name, camel_name) k##camel_name##RootIndex,
     STRONG_ROOT_LIST(ROOT_INDEX_DECLARATION)
 #undef ROOT_INDEX_DECLARATION
 
 #define STRING_INDEX_DECLARATION(name, str) k##name##RootIndex,
         INTERNALIZED_STRING_LIST(STRING_INDEX_DECLARATION)
@@ skipping 304 matching lines @@
   //
   // Support for the API.
   //
 
   void CreateApiObjects();
 
   // Implements the corresponding V8 API function.
   bool IdleNotification(double deadline_in_seconds);
   bool IdleNotification(int idle_time_in_ms);
 
+  void MemoryPressureNotification(MemoryPressureLevel level,
+                                  bool is_isolate_locked);
+
   double MonotonicallyIncreasingTimeInMs();
 
   void RecordStats(HeapStats* stats, bool take_snapshot = false);
 
   // Check new space expansion criteria and expand semispaces if it was hit.
   void CheckNewSpaceExpansionCriteria();
 
   inline bool HeapIsFullEnoughToStartIncrementalMarking(intptr_t limit) {
     if (FLAG_stress_compaction && (gc_count_ & 1) != 0) return true;
 
@@ skipping 77 matching lines @@
                           int size_in_bytes);
 
   bool deserialization_complete() const { return deserialization_complete_; }
 
   bool HasLowAllocationRate();
   bool HasHighFragmentation();
   bool HasHighFragmentation(intptr_t used, intptr_t committed);
 
   void SetOptimizeForLatency() { optimize_for_memory_usage_ = false; }
   void SetOptimizeForMemoryUsage();
-  bool ShouldOptimizeForMemoryUsage() { return optimize_for_memory_usage_; }
+  bool ShouldOptimizeForMemoryUsage() {
+    return optimize_for_memory_usage_ ||
+           memory_pressure_level_.Value() != MemoryPressureLevel::kNone;
+  }
 
   // ===========================================================================
   // Initialization. ===========================================================
   // ===========================================================================
 
   // Configure heap size in MB before setup. Return false if the heap has been
   // set up already.
   bool ConfigureHeap(int max_semi_space_size, int max_old_space_size,
                      int max_executable_size, size_t code_range_size);
   bool ConfigureHeapDefault();
@@ skipping 1142 matching lines @@
   // scavenge since last new space expansion.
   intptr_t survived_since_last_expansion_;
 
   // ... and since the last scavenge.
   intptr_t survived_last_scavenge_;
 
   // This is not the depth of nested AlwaysAllocateScope's but rather a single
   // count, as scopes can be acquired from multiple tasks (read: threads).
   AtomicNumber<size_t> always_allocate_scope_count_;
 
+  AtomicValue<MemoryPressureLevel> memory_pressure_level_;
+
   // For keeping track of context disposals.
   int contexts_disposed_;
 
   // The length of the retained_maps array at the time of context disposal.
   // This separates maps in the retained_maps array that were created before
   // and after context disposal.
   int number_of_disposed_maps_;
 
   int global_ic_age_;
 
@@ skipping 625 matching lines @@
   friend class LargeObjectSpace;
   friend class NewSpace;
   friend class PagedSpace;
   DISALLOW_COPY_AND_ASSIGN(AllocationObserver);
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_HEAP_HEAP_H_