Avoid extra GCs when deserializing during incremental marking.

src/spaces.cc

Index: src/spaces.cc
===================================================================
--- src/spaces.cc	(revision 9609)
+++ src/spaces.cc	(working copy)
@@ -1909,11 +1909,24 @@
 
 bool NewSpace::ReserveSpace(int bytes) {
   // We can't reliably unpack a partial snapshot that needs more new space
-  // space than the minimum NewSpace size.
+  // space than the minimum NewSpace size.  The limit can be set lower than
+  // the end of new space either because there is more space on the next page
+  // or because we have lowered the limit in order to get periodic incremental
+  // marking.  The most reliable way to ensure that there is linear space is
+  // to do the allocation, then rewind the limit.
   ASSERT(bytes <= InitialCapacity());
-  Address limit = allocation_info_.limit;
+  MaybeObject* maybe = AllocateRawInternal(bytes);
+  Object* object = NULL;
+  if (!maybe->ToObject(&object)) return false;
+  HeapObject* allocation = HeapObject::cast(object);
   Address top = allocation_info_.top;
-  return limit - top >= bytes;
+  if (top - bytes == allocation->address()) {

[Vyacheslav Egorov (Chromium), 2011/10/14 10:47:39]

I like to have parens around top - bytes.

+    allocation_info_.top = allocation->address();
+    return true;
+  }
+  // There may be a borderline case here where the allocation succeeded, but
+  // the limit and top have moved on to a new page.  In that case we try again.
+  return ReserveSpace(bytes);
 }