- Record cache hit rates at different levels in the compilation cache...

src/compilation-cache.cc

Index: src/compilation-cache.cc
===================================================================
--- src/compilation-cache.cc	(revision 2050)
+++ src/compilation-cache.cc	(working copy)
@@ -36,7 +36,7 @@
   // The number of script generations tell how many GCs a script can
   // survive in the compilation cache, before it will be flushed if it
   // hasn't been used.
-  NUMBER_OF_SCRIPT_GENERATIONS = 5,
+  NUMBER_OF_SCRIPT_GENERATIONS = 8,
 
   // The compilation cache consists of tables - one for each entry
   // kind plus extras for the script generations.
@@ -175,6 +175,17 @@
     }
   }
 
+  static void* script_histogram_ = StatsTable::CreateHistogram(
+      "V8.ScriptCache",
+      0,
+      NUMBER_OF_SCRIPT_GENERATIONS,
+      NUMBER_OF_SCRIPT_GENERATIONS + 1);
+
+  if (script_histogram_ != NULL) {
+    // The level NUMBER_OF_SCRIPT_GENERATIONS is equivalent to a cache miss.
+    StatsTable::AddHistogramSample(script_histogram_, generation - SCRIPT);
+  }
+
   // Once outside the manacles of the handle scope, we need to recheck
   // to see if we actually found a cached script. If so, we return a
   // handle created in the caller's handle scope.