HeapProfiler: very slow ~4min "take snapshot time" for 80MB gmail heap.

src/heap-snapshot-generator.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 157 matching lines @@
     case kHidden: return "/hidden/";
     case kObject: return "/object/";
     case kClosure: return "/closure/";
     case kString: return "/string/";
     case kCode: return "/code/";
     case kArray: return "/array/";
     case kRegExp: return "/regexp/";
     case kHeapNumber: return "/number/";
     case kNative: return "/native/";
     case kSynthetic: return "/synthetic/";
+    case kConsString: return "/concatenated string/";
+    case kSlicedString: return "/sliced string/";
     default: return "???";
   }
 }
 
 
 // It is very important to keep objects that form a heap snapshot
 // as small as possible.
 namespace {  // Avoid littering the global namespace.
 
 template <size_t ptr_size> struct SnapshotSizeConstants;
@@ skipping 587 matching lines @@
     const char* name = collection_->names()->GetName(
         GetConstructorName(JSObject::cast(object)));
     if (object->IsJSGlobalObject()) {
       const char* tag = objects_tags_.GetTag(object);
       if (tag != NULL) {
         name = collection_->names()->GetFormatted("%s / %s", name, tag);
       }
     }
     return AddEntry(object, HeapEntry::kObject, name);
   } else if (object->IsString()) {
+    String* string = String::cast(object);
+    if (string->IsConsString())
+      return AddEntry(object,
+                      HeapEntry::kConsString,
+                      "(concatenated string)");
+    if (string->IsSlicedString())
+      return AddEntry(object,
+                      HeapEntry::kSlicedString,
+                      "(sliced string)");
     return AddEntry(object,
                     HeapEntry::kString,
                     collection_->names()->GetName(String::cast(object)));
   } else if (object->IsCode()) {
     return AddEntry(object, HeapEntry::kCode, "");
   } else if (object->IsSharedFunctionInfo()) {
     String* name = String::cast(SharedFunctionInfo::cast(object)->name());
     return AddEntry(object,
                     HeapEntry::kCode,
                     collection_->names()->GetName(name));
@@ skipping 1783 matching lines @@
         JSON_A(
             JSON_S("hidden") ","
             JSON_S("array") ","
             JSON_S("string") ","
             JSON_S("object") ","
             JSON_S("code") ","
             JSON_S("closure") ","
             JSON_S("regexp") ","
             JSON_S("number") ","
             JSON_S("native") ","
-            JSON_S("synthetic")) ","
+            JSON_S("synthetic") ","
+            JSON_S("concatenated string") ","
+            JSON_S("sliced string")) ","
         JSON_S("string") ","
         JSON_S("number") ","
         JSON_S("number") ","
         JSON_S("number") ","
         JSON_S("number") ","
         JSON_S("number")) ","
     JSON_S("edge_fields") ":" JSON_A(
         JSON_S("type") ","
         JSON_S("name_or_index") ","
         JSON_S("to_node")) ","
@@ skipping 106 matching lines @@
 
 
 void HeapSnapshotJSONSerializer::SortHashMap(
     HashMap* map, List<HashMap::Entry*>* sorted_entries) {
   for (HashMap::Entry* p = map->Start(); p != NULL; p = map->Next(p))
     sorted_entries->Add(p);
   sorted_entries->Sort(SortUsingEntryValue);
 }
 
 } }  // namespace v8::internal