Add an option to control uncounted sharing in apc

Summary:
For really huge arrays, where almost every element has a refcount > 1,
tracking the shared elements adds considerable overhead, so add an
option to disable that for now.

Reviewed By: binliu19

Differential Revision: D7116889

fbshipit-source-id: 41f53ca765778bce3655945078121c1fcef48ec0

hphp/runtime/base/apc-array.cpp

@@ -52,7 +52,8 @@ APCArray::MakeSharedImpl(ArrayData* arr,
                          APCHandleLevel level,
                          A shared, B uncounted, C serialized) {
   if (level == APCHandleLevel::Outer) {
-    auto const seenArrs = std::make_unique<PointerMap>();
+    auto const seenArrs = apcExtension::ShareUncounted ?
+      std::make_unique<PointerMap>() : nullptr;
     // only need to call traverseData() on the toplevel array
     DataWalker walker(DataWalker::LookupFeature::HasObjectOrResource);
     DataWalker::DataFeature features = walker.traverseData(arr, seenArrs.get());
@@ -65,7 +66,8 @@ APCArray::MakeSharedImpl(ArrayData* arr,
         !arr->empty()) {
       auto const base_size = use_jemalloc ?
         tl_heap->getAllocated() - tl_heap->getDeallocated() :
-        getMemSize(seenArrs.get());
+        seenArrs.get() ? getMemSize(seenArrs.get()) :
+        ::HPHP::getMemSize(arr, true);
       auto const uncounted_arr = uncounted(seenArrs.get());
       auto const size = use_jemalloc ?
         tl_heap->getAllocated() - tl_heap->getDeallocated() - base_size :

hphp/runtime/ext/apc/ext_apc.cpp

@@ -197,6 +197,8 @@ void apcExtension::moduleLoad(const IniSetting::Map& ini, Hdf config) {
   Config::Bind(UseUncounted, ini, config, "Server.APC.MemModelTreadmill",
                RuntimeOption::ServerExecutionMode());
 #endif
+  Config::Bind(ShareUncounted, ini, config, "Server.APC.ShareUncounted", true);
+  if (!UseUncounted && ShareUncounted) ShareUncounted = false;
 
   IniSetting::Bind(this, IniSetting::PHP_INI_SYSTEM, "apc.enabled", &Enable);
   IniSetting::Bind(this, IniSetting::PHP_INI_SYSTEM, "apc.stat",
@@ -302,6 +304,7 @@ bool apcExtension::UseUncounted = true;
 #else
 bool apcExtension::UseUncounted = false;
 #endif
+bool apcExtension::ShareUncounted = true;
 bool apcExtension::Stat = true;
 // Different from zend default but matches what we've been returning for years
 bool apcExtension::EnableCLI = true;

hphp/runtime/ext/apc/ext_apc.h

@@ -63,6 +63,7 @@ struct apcExtension final : Extension {
   static bool FileStorageKeepFileLinked;
   static std::vector<std::string> NoTTLPrefix;
   static bool UseUncounted;
+  static bool ShareUncounted;
   static bool Stat;
   static bool EnableCLI;