Partial fix for issue 173:

- Do not keep growing the zone segment size exponentially. By putting
  an upper limit on the segment size we limit the requirements for
  contiguous memory allocation.

Review URL: http://codereview.chromium.org/12984

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@926 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/zone.cc

@@ -163,8 +163,23 @@ Address Zone::NewExpand(int size) {
   // is to avoid excessive malloc() and free() overhead.
   Segment* head = Segment::head();
   int old_size = (head == NULL) ? 0 : head->size();
-  int new_size = sizeof(Segment) + kAlignment + size + (old_size << 1);
-  if (new_size < kMinimumSegmentSize) new_size = kMinimumSegmentSize;
+  static const int kSegmentOverhead = sizeof(Segment) + kAlignment;
+  int new_size = kSegmentOverhead + size + (old_size << 1);
+  if (new_size < kMinimumSegmentSize) {
+    new_size = kMinimumSegmentSize;
+  } else if (new_size > kMaximumSegmentSize) {
+    // Limit the size of new segments to avoid growing the segment size
+    // exponentially, thus putting pressure on contiguous virtual address
+    // space.
+    if (size > (kMaximumSegmentSize - kSegmentOverhead)) {
+      // Make sure to allocate a segment at large enough to hold the requested
+      // size.
+      new_size = kSegmentOverhead + size;
+    } else {
+      // Allocate a new segment of maximum size.
+      new_size = kMaximumSegmentSize;
+    }
+  }
   Segment* segment = Segment::New(new_size);
   if (segment == NULL) V8::FatalProcessOutOfMemory("Zone");
 

src/zone.h

@@ -74,6 +74,9 @@ class Zone {
 
   // Never allocate segments smaller than this size in bytes.
   static const int kMinimumSegmentSize = 8 * KB;
+  
+  // Never allocate segments larger than this size in bytes.
+  static const int kMaximumSegmentSize = 1 * MB;
 
   // Never keep segments larger than this size in bytes around.
   static const int kMaximumKeptSegmentSize = 64 * KB;