Version 5.6.1.1 (cherry-pick)

src/zone/zone.h

Index: src/zone/zone.h
diff --git a/src/zone/zone.h b/src/zone/zone.h
index 9a17d5d04627c3531b1890492e31430a73abb546..0bf7f28a8442f87823f10a96363360d7d933d54d 100644
--- a/src/zone/zone.h
+++ b/src/zone/zone.h
@@ -25,7 +25,7 @@ namespace internal {
 //
 // Note: There is no need to initialize the Zone; the first time an
 // allocation is attempted, a segment of memory will be requested
-// through the allocator.
+// through a call to malloc().
 //
 // Note: The implementation is inherently not thread safe. Do not use
 // from multi-threaded code.
@@ -44,6 +44,14 @@ class V8_EXPORT_PRIVATE Zone final {
     return static_cast<T*>(New(length * sizeof(T)));
   }
 
+  // Deletes all objects and free all memory allocated in the Zone. Keeps one
+  // small (size <= kMaximumKeptSegmentSize) segment around if it finds one.
+  void DeleteAll();
+
+  // Deletes the last small segment kept around by DeleteAll(). You
+  // may no longer allocate in the Zone after a call to this method.
+  void DeleteKeptSegment();
+
   // Returns true if more memory has been allocated in zones than
   // the limit allows.
   bool excess_allocation() const {
@@ -72,12 +80,12 @@ class V8_EXPORT_PRIVATE Zone final {
   // Never allocate segments larger than this size in bytes.
   static const size_t kMaximumSegmentSize = 1 * MB;
 
+  // Never keep segments larger than this size in bytes around.
+  static const size_t kMaximumKeptSegmentSize = 64 * KB;
+
   // Report zone excess when allocation exceeds this limit.
   static const size_t kExcessLimit = 256 * MB;
 
-  // Deletes all objects and free all memory allocated in the Zone.
-  void DeleteAll();
-
   // The number of bytes allocated in this zone so far.
   size_t allocation_size_;
 
@@ -94,7 +102,7 @@ class V8_EXPORT_PRIVATE Zone final {
 
   // Creates a new segment, sets it size, and pushes it to the front
   // of the segment chain. Returns the new segment.
-  inline Segment* NewSegment(size_t requested_size);
+  inline Segment* NewSegment(size_t size);
 
   // The free region in the current (front) segment is represented as
   // the half-open interval [position, limit). The 'position' variable
@@ -126,6 +134,19 @@ class ZoneObject {
   void operator delete(void* pointer, Zone* zone) { UNREACHABLE(); }
 };
 
+// The ZoneScope is used to automatically call DeleteAll() on a
+// Zone when the ZoneScope is destroyed (i.e. goes out of scope)
+class ZoneScope final {
+ public:
+  explicit ZoneScope(Zone* zone) : zone_(zone) {}
+  ~ZoneScope() { zone_->DeleteAll(); }
+
+  Zone* zone() const { return zone_; }
+
+ private:
+  Zone* zone_;
+};
+
 // The ZoneAllocationPolicy is used to specialize generic data
 // structures to allocate themselves and their elements in the Zone.
 class ZoneAllocationPolicy final {