- Reduced the maximum capacity of a semi space from 8MB to 4MB.

- Changed the semi space growth policy from doubling to increasing by 50%.
This slows down V8BenchmarkSuite with 1.32% but reduces the memory footprint with 8MB per V8 instance.

Review URL: http://codereview.chromium.org/164397

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@2667 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/heap.cc

@@ -74,7 +74,7 @@ int Heap::semispace_size_  = 512*KB;
 int Heap::old_generation_size_ = 128*MB;
 int Heap::initial_semispace_size_ = 128*KB;
 #else
-int Heap::semispace_size_  = 8*MB;
+int Heap::semispace_size_  = 4*MB;
 int Heap::old_generation_size_ = 512*MB;
 int Heap::initial_semispace_size_ = 512*KB;
 #endif
@@ -641,11 +641,11 @@ void Heap::Scavenge() {
 
   if (new_space_.Capacity() < new_space_.MaximumCapacity() &&
       survived_since_last_expansion_ > new_space_.Capacity()) {
-    // Double the size of new space if there is room to grow and enough
+    // Grow the size of new space if there is room to grow and enough
     // data has survived scavenge since the last expansion.
-    // TODO(1240712): NewSpace::Double has a return value which is
+    // TODO(1240712): NewSpace::Grow has a return value which is
     // ignored here.
-    new_space_.Double();
+    new_space_.Grow();
     survived_since_last_expansion_ = 0;
   }
 

src/spaces.cc

@@ -963,13 +963,13 @@ void NewSpace::Flip() {
 }
 
 
-bool NewSpace::Double() {
-  ASSERT(capacity_ <= maximum_capacity_ / 2);
+bool NewSpace::Grow() {
+  ASSERT(capacity_ < maximum_capacity_);
   // TODO(1240712): Failure to double the from space can result in
   // semispaces of different sizes.  In the event of that failure, the
   // to space doubling should be rolled back before returning false.
-  if (!to_space_.Double() || !from_space_.Double()) return false;
-  capacity_ *= 2;
+  if (!to_space_.Grow() || !from_space_.Grow()) return false;
+  capacity_ = to_space_.Capacity() + from_space_.Capacity();
   allocation_info_.limit = to_space_.high();
   ASSERT_SEMISPACE_ALLOCATION_INFO(allocation_info_, to_space_);
   return true;
@@ -1074,11 +1074,16 @@ void SemiSpace::TearDown() {
 }
 
 
-bool SemiSpace::Double() {
-  if (!MemoryAllocator::CommitBlock(high(), capacity_, executable())) {
+bool SemiSpace::Grow() {
+  // Commit 50% extra space but only up to maximum capacity.
+  int extra = capacity_/2;
+  if (capacity_ + extra > maximum_capacity_) {
+    extra = maximum_capacity_ - capacity_;
+  }
+  if (!MemoryAllocator::CommitBlock(high(), extra, executable())) {
     return false;
   }
-  capacity_ *= 2;
+  capacity_ += extra;
   return true;
 }
 

src/spaces.h

@@ -997,11 +997,11 @@ class SemiSpace : public Space {
   // True if the space has been set up but not torn down.
   bool HasBeenSetup() { return start_ != NULL; }
 
-  // Double the size of the semispace by committing extra virtual memory.
+  // Grow the size of the semispace by committing extra virtual memory.
   // Assumes that the caller has checked that the semispace has not reached
   // its maximum capacity (and thus there is space available in the reserved
   // address range to grow).
-  bool Double();
+  bool Grow();
 
   // Returns the start address of the space.
   Address low() { return start_; }
@@ -1040,6 +1040,9 @@ class SemiSpace : public Space {
   virtual void Verify();
 #endif
 
+  // Returns the current capacity of the semi space.
+  int Capacity() { return capacity_; }
+
  private:
   // The current and maximum capacity of the space.
   int capacity_;
@@ -1131,9 +1134,9 @@ class NewSpace : public Space {
   // Flip the pair of spaces.
   void Flip();
 
-  // Doubles the capacity of the semispaces.  Assumes that they are not at
+  // Grow the capacity of the semispaces.  Assumes that they are not at
   // their maximum capacity.  Returns a flag indicating success or failure.
-  bool Double();
+  bool Grow();
 
   // True if the address or object lies in the address range of either
   // semispace (not necessarily below the allocation pointer).