[heap] Evacuation for young generation

src/heap/spaces.h

Index: src/heap/spaces.h
diff --git a/src/heap/spaces.h b/src/heap/spaces.h
index 5a57a30a30dd3a7d78fd3999d5a4556005725133..539df2543f56f6380583a2afd833f76110708cc0 100644
--- a/src/heap/spaces.h
+++ b/src/heap/spaces.h
@@ -524,6 +524,8 @@ class MemoryChunk {
            !IsFlagSet(COMPACTION_WAS_ABORTED);
   }
 
+  bool CanUseForAllocation() { return CanAllocate() && !NeverEvacuate(); }
+
   Executability executable() {
     return IsFlagSet(IS_EXECUTABLE) ? EXECUTABLE : NOT_EXECUTABLE;
   }
@@ -1610,28 +1612,28 @@ class AllocationStats BASE_EMBEDDED {
 
   // Zero out all the allocation statistics (i.e., no capacity).
   void Clear() {
-    capacity_ = 0;
-    max_capacity_ = 0;
-    size_ = 0;
+    capacity_.SetValue(0);
+    max_capacity_.SetValue(0);
+    size_.SetValue(0);
   }
 
-  void ClearSize() { size_ = capacity_; }
+  void ClearSize() { size_.SetValue(capacity_.Value()); }
 
   // Accessors for the allocation statistics.
-  size_t Capacity() { return capacity_; }
-  size_t MaxCapacity() { return max_capacity_; }
-  size_t Size() { return size_; }
+  size_t Capacity() { return capacity_.Value(); }
+  size_t MaxCapacity() { return max_capacity_.Value(); }
+  size_t Size() { return size_.Value(); }
 
   // Grow the space by adding available bytes.  They are initially marked as
   // being in use (part of the size), but will normally be immediately freed,
   // putting them on the free list and removing them from size_.
   void ExpandSpace(size_t bytes) {
-    DCHECK_GE(size_ + bytes, size_);
-    DCHECK_GE(capacity_ + bytes, capacity_);
-    capacity_ += bytes;
-    size_ += bytes;
-    if (capacity_ > max_capacity_) {
-      max_capacity_ = capacity_;
+    DCHECK_GE(size_.Value() + bytes, size_.Value());
+    DCHECK_GE(capacity_.Value() + bytes, capacity_.Value());
+    capacity_.Increment(bytes);
+    size_.Increment(bytes);
+    if (capacity_.Value() > max_capacity_.Value()) {
+      max_capacity_.SetValue(capacity_.Value());
     }
   }
 
@@ -1639,54 +1641,54 @@ class AllocationStats BASE_EMBEDDED {
   // during sweeping, bytes have been marked as being in use (part of the size)
   // and are hereby freed.
   void ShrinkSpace(size_t bytes) {
-    DCHECK_GE(capacity_, bytes);
-    DCHECK_GE(size_, bytes);
-    capacity_ -= bytes;
-    size_ -= bytes;
+    DCHECK_GE(capacity_.Value(), bytes);
+    DCHECK_GE(size_.Value(), bytes);
+    capacity_.Decrement(bytes);
+    size_.Decrement(bytes);
   }
 
   void AllocateBytes(size_t bytes) {
-    DCHECK_GE(size_ + bytes, size_);
-    size_ += bytes;
+    DCHECK_GE(size_.Value() + bytes, size_.Value());
+    size_.Increment(bytes);
   }
 
   void DeallocateBytes(size_t bytes) {
-    DCHECK_GE(size_, bytes);
-    size_ -= bytes;
+    DCHECK_GE(size_.Value(), bytes);
+    size_.Decrement(bytes);
   }
 
   void DecreaseCapacity(size_t bytes) {
-    DCHECK_GE(capacity_, bytes);
-    DCHECK_GE(capacity_ - bytes, size_);
-    capacity_ -= bytes;
+    DCHECK_GE(capacity_.Value(), bytes);
+    DCHECK_GE(capacity_.Value() - bytes, size_.Value());
+    capacity_.Decrement(bytes);
   }
 
   void IncreaseCapacity(size_t bytes) {
-    DCHECK_GE(capacity_ + bytes, capacity_);
-    capacity_ += bytes;
+    DCHECK_GE(capacity_.Value() + bytes, capacity_.Value());
+    capacity_.Increment(bytes);
   }
 
   // Merge |other| into |this|.
   void Merge(const AllocationStats& other) {
-    DCHECK_GE(capacity_ + other.capacity_, capacity_);
-    DCHECK_GE(size_ + other.size_, size_);
-    capacity_ += other.capacity_;
-    size_ += other.size_;
-    if (other.max_capacity_ > max_capacity_) {
-      max_capacity_ = other.max_capacity_;
+    DCHECK_GE(capacity_.Value() + other.capacity_.Value(), capacity_.Value());
+    DCHECK_GE(size_.Value() + other.size_.Value(), size_.Value());
+    capacity_.Increment(other.capacity_.Value());
+    size_.Increment(other.size_.Value());
+    if (other.max_capacity_.Value() > max_capacity_.Value()) {
+      max_capacity_.SetValue(other.max_capacity_.Value());
     }
   }
 
  private:
   // |capacity_|: The number of object-area bytes (i.e., not including page
   // bookkeeping structures) currently in the space.
-  size_t capacity_;
+  base::AtomicNumber<size_t> capacity_;
 
   // |max_capacity_|: The maximum capacity ever observed.
-  size_t max_capacity_;
+  base::AtomicNumber<size_t> max_capacity_;
 
   // |size_|: The number of allocated bytes.
-  size_t size_;
+  base::AtomicNumber<size_t> size_;
 };
 
 // A free list maintaining free blocks of memory. The free list is organized in
@@ -1952,6 +1954,10 @@ class V8_EXPORT_PRIVATE PagedSpace : NON_EXPORTED_BASE(public Space) {
  public:
   typedef PageIterator iterator;
 
+  // Reuse a page for allocation only if it has at least {kPageReuseThreshold}
+  // memory available in its FreeList.
+  static const size_t kPageReuseThreshold = 4 * KB;
+
   static const intptr_t kCompactionMemoryWanted = 500 * KB;
 
   // Creates a space with an id.
@@ -2158,6 +2164,9 @@ class V8_EXPORT_PRIVATE PagedSpace : NON_EXPORTED_BASE(public Space) {
 
   std::unique_ptr<ObjectIterator> GetObjectIterator() override;
 
+  Page* RemovePageSafe();
+  void AddPage(Page* page);
+
  protected:
   // PagedSpaces that should be included in snapshots have different, i.e.,
   // smaller, initial pages.