Changeset 233039 in webkit for trunk/Source/JavaScriptCore/bytecode/UnlinkedFunctionExecutable.h

Timestamp:

Jun 21, 2018, 8:09:40 AM (7 years ago)

Author:

[email protected]

Message:

Use IsoCellSets to track Executables with clearable code.
​https://bugs.webkit.org/show_bug.cgi?id=186877

Reviewed by Filip Pizlo.

Here’s an example of the results that this fix may yield:

1. The workload: load cnn.com, wait for it to fully load, scroll down and up.
2. Statistics on memory touched and memory freed by VM::deleteAllCode():

Visiting Executables:

Old New

Number of objects visited: 70897 14264
Number of objects with deletable code: 14264 (20.1%) 14264 (100%)
Number of memory pages visited: 3224 1602
Number of memory pages with deletable code: 1602 (49.7%) 1602 (100%)

Visitng UnlinkedFunctionExecutables:

Old New

Number of objects visited: 105454 17231
Number of objects with deletable code: 42319 (20.1%) 17231 (100%)
Number of memory pages visited: 4796 1349
Number of memory pages with deletable code: 4013 (83.7%) 1349 (100%)

The number of objects differ because the old code only visit unlinked

executables indirectly via linked executables, whereas the new behavior visit
all unlinked executables with deletable code directly. This means:

1. we used to not visit unlinked executables that have not been linked yet i.e. deleteAllCode() may not delete all code (especially code that is not used).
2. we had to visit all linked executables to check if they of type FunctionExecutable, before going on to visit their unlinked executable, and this includes the ones that do not have deletable code. This means that we would touch more memory in the process.

Both of these these issues are now fixed with the new code.

This code was tested with manually inserted instrumentation to track the above
statistics. It is not feasible to write an automated test for this without
leaving a lot of invasive instrumentation in the code.

• bytecode/UnlinkedFunctionExecutable.cpp:

(JSC::UnlinkedFunctionExecutable::unlinkedCodeBlockFor):

• bytecode/UnlinkedFunctionExecutable.h:
• heap/CodeBlockSetInlines.h:

(JSC::CodeBlockSet::iterateViaSubspaces):

• heap/Heap.cpp:

(JSC::Heap::deleteAllCodeBlocks):
(JSC::Heap::deleteAllUnlinkedCodeBlocks):
(JSC::Heap::deleteUnmarkedCompiledCode):
(JSC::Heap::clearUnmarkedExecutables): Deleted.
(JSC::Heap::addExecutable): Deleted.

• heap/Heap.h:
• runtime/DirectEvalExecutable.h:

• runtime/ExecutableBase.cpp:

(JSC::ExecutableBase::hasClearableCode const):

• this is written based on the implementation of ExecutableBase::clearCode().

• runtime/ExecutableBase.h:
• runtime/FunctionExecutable.h:
• runtime/IndirectEvalExecutable.h:
• runtime/ModuleProgramExecutable.h:
• runtime/ProgramExecutable.h:
• runtime/ScriptExecutable.cpp:

(JSC::ScriptExecutable::clearCode):
(JSC::ScriptExecutable::installCode):

• runtime/ScriptExecutable.h:

(JSC::ScriptExecutable::finishCreation):

• runtime/VM.cpp:

(JSC::VM::VM):

• runtime/VM.h:

(JSC::VM::ScriptExecutableSpaceAndSet::ScriptExecutableSpaceAndSet):
(JSC::VM::ScriptExecutableSpaceAndSet::clearableCodeSetFor):
(JSC::VM::forEachScriptExecutableSpace):
(JSC::VM::UnlinkedFunctionExecutableSpaceAndSet::UnlinkedFunctionExecutableSpaceAndSet):
(JSC::VM::UnlinkedFunctionExecutableSpaceAndSet::clearableCodeSetFor):

File:

• trunk/Source/JavaScriptCore/bytecode/UnlinkedFunctionExecutable.h (modified) (2 diffs)

trunk/Source/JavaScriptCore/bytecode/UnlinkedFunctionExecutable.h

@@ -59 +59 @@
     static const unsigned StructureFlags = Base::StructureFlags | StructureIsImmortal;
 
+    template<typename CellType>
+    static IsoSubspace* subspaceFor(VM& vm)
+    {
+        return &vm.unlinkedFunctionExecutableSpace.space;
+    }
+
     static UnlinkedFunctionExecutable* create(VM* vm, const SourceCode& source, FunctionMetadataNode* node, UnlinkedFunctionKind unlinkedFunctionKind, ConstructAbility constructAbility, JSParserScriptMode scriptMode, VariableEnvironment& parentScopeTDZVariables, DerivedContextType derivedContextType, bool isBuiltinDefaultClassConstructor = false)
     {
@@ -106 +112 @@
     JS_EXPORT_PRIVATE FunctionExecutable* link(VM&, const SourceCode& parentSource, std::optional<int> overrideLineNumber = std::nullopt, Intrinsic = NoIntrinsic);
 
-    void clearCode()
+    void clearCode(VM& vm)
     {
         m_unlinkedCodeBlockForCall.clear();
         m_unlinkedCodeBlockForConstruct.clear();
+        vm.unlinkedFunctionExecutableSpace.clearableCodeSet.remove(this);
     }