Lower heap size limits on systems that are short of virtual memory.

src/heap.cc

Index: src/heap.cc
===================================================================
--- src/heap.cc	(revision 8132)
+++ src/heap.cc	(working copy)
@@ -152,6 +152,29 @@
   max_semispace_size_ = reserved_semispace_size_ = V8_MAX_SEMISPACE_SIZE;
 #endif
 
+  intptr_t max_virtual = OS::MaxVirtualMemory();
+
+  if (max_virtual > 0) {
+    // If we have limits on the amount of virtual memory we can use then we may
+    // be forced to lower the allocation limits.  We reserve one quarter of the
+    // memory for young space and off-heap data.  The rest is distributed as
+    // described below.
+    if (code_range_size_ > 0) {

[Kasper Lund, 2011/06/01 08:46:04]

Maybe introduce two local variables, half and quarter, and use them instead of
the repeated max_virtual >> {1,2}.

+      // Reserve a quarter of the memory for the code range.  The old space
+      // heap gets the remaining half.  There is some unavoidable double
+      // counting going on here since the heap size is measured in committed
+      // virtual memory and the code range is only reserved virtual memory.
+      code_range_size_ = Min(code_range_size_, max_virtual >> 2);
+      max_old_generation_size_ =
+          Min(max_old_generation_size_, max_virtual >> 1);
+    } else {
+      // Reserve three quarters of the memory for the old space heap including
+      // the executable code.
+      max_old_generation_size_ = Min(max_old_generation_size_,
+                                     (max_virtual >> 2) + (max_virtual >> 1));
+    }
+  }
+
   memset(roots_, 0, sizeof(roots_[0]) * kRootListLength);
   global_contexts_list_ = NULL;
   mark_compact_collector_.heap_ = this;