Push memory reduction changes to 1.2 branch.

src/spaces.h

Index: src/spaces.h
===================================================================
--- src/spaces.h	(revision 2883)
+++ src/spaces.h	(working copy)
@@ -432,9 +432,13 @@
 
   // Due to encoding limitation, we can only have 8K chunks.
   static const int kMaxNofChunks = 1 << Page::kPageSizeBits;
-  // If a chunk has at least 32 pages, the maximum heap size is about
-  // 8 * 1024 * 32 * 8K = 2G bytes.
-  static const int kPagesPerChunk = 64;
+  // If a chunk has at least 16 pages, the maximum heap size is about
+  // 8k * 8K * 16 = 1G bytes.
+#ifdef V8_TARGET_ARCH_X64
+  static const int kPagesPerChunk = 32;
+#else
+  static const int kPagesPerChunk = 16;
+#endif
   static const int kChunkSize = kPagesPerChunk * Page::kPageSize;
 
  private: