Avoid fragmenting address space on small windows systems.

Source/wtf/PageAllocator.cpp

Index: Source/wtf/PageAllocator.cpp
diff --git a/Source/wtf/PageAllocator.cpp b/Source/wtf/PageAllocator.cpp
index 182a76ce2b99e1b5bf9e122ba1c2a134b9c9003d..984dd9d1b22c2d7fa6689c4492e0ce19a76b2f39 100644
--- a/Source/wtf/PageAllocator.cpp
+++ b/Source/wtf/PageAllocator.cpp
@@ -58,6 +58,29 @@
 
 namespace WTF {
 
+#if OS(WIN)
+
+static bool shouldUseAddressHint()
+{
+#if !CPU(X86_64)
+    // Determine if userspace is limited to 2 GB.
+    static bool architectureKnown = false;
+    static bool useHint = true;
+    if (!architectureKnown) {
+        SYSTEM_INFO systemInfo = { 0 };
+        ::GetNativeSystemInfo(&systemInfo);
+        if (systemInfo.wProcessorArchitecture == PROCESSOR_ARCHITECTURE_INTEL)

[Chris Evans, 2014/07/18 18:21:00]

Ah. Maybe I get it now. Is the 3G/1G for Windows 32-bit processes restricted to
when the underlying CPU is x86_64? I still find it a bit unclear.

Would it be clearer to use the lpMaximumApplicationAddress field of this
structure? If it is over 0x80000000 then we can use the hints, otherwise not?

+            useHint = false;
+        architectureKnown = true;
+    }
+    return useHint;
+#else // !CPU(X86_64)
+    return true;
+#endif // !CPU(X86_64)
+}
+
+#endif // OS(WIN)
+
 // This simple internal function wraps the OS-specific page allocation call so
 // that it behaves consistently: the address is a hint and if it cannot be used,
 // the allocation will be placed elsewhere.
@@ -65,9 +88,10 @@ static void* systemAllocPages(void* addr, size_t len)
 {
     ASSERT(!(len & kPageAllocationGranularityOffsetMask));
     ASSERT(!(reinterpret_cast<uintptr_t>(addr) & kPageAllocationGranularityOffsetMask));
-    void* ret;
+    void* ret = 0;
 #if OS(WIN)
-    ret = VirtualAlloc(addr, len, MEM_RESERVE | MEM_COMMIT, PAGE_READWRITE);
+    if (shouldUseAddressHint())
+        ret = VirtualAlloc(addr, len, MEM_RESERVE | MEM_COMMIT, PAGE_READWRITE);
     if (!ret)
         ret = VirtualAlloc(0, len, MEM_RESERVE | MEM_COMMIT, PAGE_READWRITE);
 #else