// Copyright 2006-2008 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 // with the distribution. // * Neither the name of Google Inc. nor the names of its // contributors may be used to endorse or promote products derived // from this software without specific prior written permission. // // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. #include "v8.h" #include "execution.h" #include "heap-profiler.h" #include "global-handles.h" #include "ic-inl.h" #include "mark-compact.h" #include "stub-cache.h" namespace v8 { namespace internal { // ------------------------------------------------------------------------- // MarkCompactCollector bool MarkCompactCollector::force_compaction_ = false; bool MarkCompactCollector::compacting_collection_ = false; bool MarkCompactCollector::compact_on_next_gc_ = false; int MarkCompactCollector::previous_marked_count_ = 0; GCTracer* MarkCompactCollector::tracer_ = NULL; #ifdef DEBUG MarkCompactCollector::CollectorState MarkCompactCollector::state_ = IDLE; // Counters used for debugging the marking phase of mark-compact or mark-sweep // collection. int MarkCompactCollector::live_bytes_ = 0; int MarkCompactCollector::live_young_objects_size_ = 0; int MarkCompactCollector::live_old_data_objects_size_ = 0; int MarkCompactCollector::live_old_pointer_objects_size_ = 0; int MarkCompactCollector::live_code_objects_size_ = 0; int MarkCompactCollector::live_map_objects_size_ = 0; int MarkCompactCollector::live_cell_objects_size_ = 0; int MarkCompactCollector::live_lo_objects_size_ = 0; #endif void MarkCompactCollector::CollectGarbage() { // Make sure that Prepare() has been called. The individual steps below will // update the state as they proceed. ASSERT(state_ == PREPARE_GC); // Prepare has selected whether to compact the old generation or not. // Tell the tracer. if (IsCompacting()) tracer_->set_is_compacting(); MarkLiveObjects(); if (FLAG_collect_maps) ClearNonLiveTransitions(); SweepLargeObjectSpace(); if (IsCompacting()) { GCTracer::Scope gc_scope(tracer_, GCTracer::Scope::MC_COMPACT); EncodeForwardingAddresses(); UpdatePointers(); RelocateObjects(); } else { SweepSpaces(); } Finish(); // Save the count of marked objects remaining after the collection and // null out the GC tracer. previous_marked_count_ = tracer_->marked_count(); ASSERT(previous_marked_count_ == 0); tracer_ = NULL; } void MarkCompactCollector::Prepare(GCTracer* tracer) { // Rather than passing the tracer around we stash it in a static member // variable. tracer_ = tracer; #ifdef DEBUG ASSERT(state_ == IDLE); state_ = PREPARE_GC; #endif ASSERT(!FLAG_always_compact || !FLAG_never_compact); compacting_collection_ = FLAG_always_compact || force_compaction_ || compact_on_next_gc_; compact_on_next_gc_ = false; if (FLAG_never_compact) compacting_collection_ = false; if (!Heap::map_space()->MapPointersEncodable()) compacting_collection_ = false; if (FLAG_collect_maps) CreateBackPointers(); PagedSpaces spaces; for (PagedSpace* space = spaces.next(); space != NULL; space = spaces.next()) { space->PrepareForMarkCompact(compacting_collection_); } #ifdef DEBUG live_bytes_ = 0; live_young_objects_size_ = 0; live_old_pointer_objects_size_ = 0; live_old_data_objects_size_ = 0; live_code_objects_size_ = 0; live_map_objects_size_ = 0; live_cell_objects_size_ = 0; live_lo_objects_size_ = 0; #endif } void MarkCompactCollector::Finish() { #ifdef DEBUG ASSERT(state_ == SWEEP_SPACES || state_ == RELOCATE_OBJECTS); state_ = IDLE; #endif // The stub cache is not traversed during GC; clear the cache to // force lazy re-initialization of it. This must be done after the // GC, because it relies on the new address of certain old space // objects (empty string, illegal builtin). StubCache::Clear(); ExternalStringTable::CleanUp(); // If we've just compacted old space there's no reason to check the // fragmentation limit. Just return. if (HasCompacted()) return; // We compact the old generation on the next GC if it has gotten too // fragmented (ie, we could recover an expected amount of space by // reclaiming the waste and free list blocks). static const int kFragmentationLimit = 15; // Percent. static const int kFragmentationAllowed = 1 * MB; // Absolute. int old_gen_recoverable = 0; int old_gen_used = 0; OldSpaces spaces; for (OldSpace* space = spaces.next(); space != NULL; space = spaces.next()) { old_gen_recoverable += space->Waste() + space->AvailableFree(); old_gen_used += space->Size(); } int old_gen_fragmentation = static_cast((old_gen_recoverable * 100.0) / old_gen_used); if (old_gen_fragmentation > kFragmentationLimit && old_gen_recoverable > kFragmentationAllowed) { compact_on_next_gc_ = true; } } // ------------------------------------------------------------------------- // Phase 1: tracing and marking live objects. // before: all objects are in normal state. // after: a live object's map pointer is marked as '00'. // Marking all live objects in the heap as part of mark-sweep or mark-compact // collection. Before marking, all objects are in their normal state. After // marking, live objects' map pointers are marked indicating that the object // has been found reachable. // // The marking algorithm is a (mostly) depth-first (because of possible stack // overflow) traversal of the graph of objects reachable from the roots. It // uses an explicit stack of pointers rather than recursion. The young // generation's inactive ('from') space is used as a marking stack. The // objects in the marking stack are the ones that have been reached and marked // but their children have not yet been visited. // // The marking stack can overflow during traversal. In that case, we set an // overflow flag. When the overflow flag is set, we continue marking objects // reachable from the objects on the marking stack, but no longer push them on // the marking stack. Instead, we mark them as both marked and overflowed. // When the stack is in the overflowed state, objects marked as overflowed // have been reached and marked but their children have not been visited yet. // After emptying the marking stack, we clear the overflow flag and traverse // the heap looking for objects marked as overflowed, push them on the stack, // and continue with marking. This process repeats until all reachable // objects have been marked. static MarkingStack marking_stack; static inline HeapObject* ShortCircuitConsString(Object** p) { // Optimization: If the heap object pointed to by p is a non-symbol // cons string whose right substring is Heap::empty_string, update // it in place to its left substring. Return the updated value. // // Here we assume that if we change *p, we replace it with a heap object // (ie, the left substring of a cons string is always a heap object). // // The check performed is: // object->IsConsString() && !object->IsSymbol() && // (ConsString::cast(object)->second() == Heap::empty_string()) // except the maps for the object and its possible substrings might be // marked. HeapObject* object = HeapObject::cast(*p); MapWord map_word = object->map_word(); map_word.ClearMark(); InstanceType type = map_word.ToMap()->instance_type(); if ((type & kShortcutTypeMask) != kShortcutTypeTag) return object; Object* second = reinterpret_cast(object)->unchecked_second(); if (second != Heap::raw_unchecked_empty_string()) { return object; } // Since we don't have the object's start, it is impossible to update the // page dirty marks. Therefore, we only replace the string with its left // substring when page dirty marks do not change. Object* first = reinterpret_cast(object)->unchecked_first(); if (!Heap::InNewSpace(object) && Heap::InNewSpace(first)) return object; *p = first; return HeapObject::cast(first); } // Helper class for marking pointers in HeapObjects. class MarkingVisitor : public ObjectVisitor { public: void VisitPointer(Object** p) { MarkObjectByPointer(p); } void VisitPointers(Object** start, Object** end) { // Mark all objects pointed to in [start, end). const int kMinRangeForMarkingRecursion = 64; if (end - start >= kMinRangeForMarkingRecursion) { if (VisitUnmarkedObjects(start, end)) return; // We are close to a stack overflow, so just mark the objects. } for (Object** p = start; p < end; p++) MarkObjectByPointer(p); } void VisitCodeTarget(RelocInfo* rinfo) { ASSERT(RelocInfo::IsCodeTarget(rinfo->rmode())); Code* code = Code::GetCodeFromTargetAddress(rinfo->target_address()); if (FLAG_cleanup_ics_at_gc && code->is_inline_cache_stub()) { IC::Clear(rinfo->pc()); // Please note targets for cleared inline cached do not have to be // marked since they are contained in Heap::non_monomorphic_cache(). } else { MarkCompactCollector::MarkObject(code); } } void VisitDebugTarget(RelocInfo* rinfo) { ASSERT((RelocInfo::IsJSReturn(rinfo->rmode()) && rinfo->IsPatchedReturnSequence()) || (RelocInfo::IsDebugBreakSlot(rinfo->rmode()) && rinfo->IsPatchedDebugBreakSlotSequence())); HeapObject* code = Code::GetCodeFromTargetAddress(rinfo->call_address()); MarkCompactCollector::MarkObject(code); } private: // Mark object pointed to by p. void MarkObjectByPointer(Object** p) { if (!(*p)->IsHeapObject()) return; HeapObject* object = ShortCircuitConsString(p); MarkCompactCollector::MarkObject(object); } // Tells whether the mark sweep collection will perform compaction. bool IsCompacting() { return MarkCompactCollector::IsCompacting(); } // Visit an unmarked object. void VisitUnmarkedObject(HeapObject* obj) { #ifdef DEBUG ASSERT(Heap::Contains(obj)); ASSERT(!obj->IsMarked()); #endif Map* map = obj->map(); MarkCompactCollector::SetMark(obj); // Mark the map pointer and the body. MarkCompactCollector::MarkObject(map); obj->IterateBody(map->instance_type(), obj->SizeFromMap(map), this); } // Visit all unmarked objects pointed to by [start, end). // Returns false if the operation fails (lack of stack space). inline bool VisitUnmarkedObjects(Object** start, Object** end) { // Return false is we are close to the stack limit. StackLimitCheck check; if (check.HasOverflowed()) return false; // Visit the unmarked objects. for (Object** p = start; p < end; p++) { if (!(*p)->IsHeapObject()) continue; HeapObject* obj = HeapObject::cast(*p); if (obj->IsMarked()) continue; VisitUnmarkedObject(obj); } return true; } }; // Visitor class for marking heap roots. class RootMarkingVisitor : public ObjectVisitor { public: void VisitPointer(Object** p) { MarkObjectByPointer(p); } void VisitPointers(Object** start, Object** end) { for (Object** p = start; p < end; p++) MarkObjectByPointer(p); } MarkingVisitor* stack_visitor() { return &stack_visitor_; } private: MarkingVisitor stack_visitor_; void MarkObjectByPointer(Object** p) { if (!(*p)->IsHeapObject()) return; // Replace flat cons strings in place. HeapObject* object = ShortCircuitConsString(p); if (object->IsMarked()) return; Map* map = object->map(); // Mark the object. MarkCompactCollector::SetMark(object); // Mark the map pointer and body, and push them on the marking stack. MarkCompactCollector::MarkObject(map); object->IterateBody(map->instance_type(), object->SizeFromMap(map), &stack_visitor_); // Mark all the objects reachable from the map and body. May leave // overflowed objects in the heap. MarkCompactCollector::EmptyMarkingStack(&stack_visitor_); } }; // Helper class for pruning the symbol table. class SymbolTableCleaner : public ObjectVisitor { public: SymbolTableCleaner() : pointers_removed_(0) { } virtual void VisitPointers(Object** start, Object** end) { // Visit all HeapObject pointers in [start, end). for (Object** p = start; p < end; p++) { if ((*p)->IsHeapObject() && !HeapObject::cast(*p)->IsMarked()) { // Check if the symbol being pruned is an external symbol. We need to // delete the associated external data as this symbol is going away. // Since no objects have yet been moved we can safely access the map of // the object. if ((*p)->IsExternalString()) { Heap::FinalizeExternalString(String::cast(*p)); } // Set the entry to null_value (as deleted). *p = Heap::raw_unchecked_null_value(); pointers_removed_++; } } } int PointersRemoved() { return pointers_removed_; } private: int pointers_removed_; }; void MarkCompactCollector::MarkUnmarkedObject(HeapObject* object) { ASSERT(!object->IsMarked()); ASSERT(Heap::Contains(object)); if (object->IsMap()) { Map* map = Map::cast(object); if (FLAG_cleanup_caches_in_maps_at_gc) { map->ClearCodeCache(); } SetMark(map); if (FLAG_collect_maps && map->instance_type() >= FIRST_JS_OBJECT_TYPE && map->instance_type() <= JS_FUNCTION_TYPE) { MarkMapContents(map); } else { marking_stack.Push(map); } } else { SetMark(object); marking_stack.Push(object); } } void MarkCompactCollector::MarkMapContents(Map* map) { MarkDescriptorArray(reinterpret_cast( *HeapObject::RawField(map, Map::kInstanceDescriptorsOffset))); // Mark the Object* fields of the Map. // Since the descriptor array has been marked already, it is fine // that one of these fields contains a pointer to it. MarkingVisitor visitor; // Has no state or contents. visitor.VisitPointers(HeapObject::RawField(map, Map::kPointerFieldsBeginOffset), HeapObject::RawField(map, Map::kPointerFieldsEndOffset)); } void MarkCompactCollector::MarkDescriptorArray( DescriptorArray* descriptors) { if (descriptors->IsMarked()) return; // Empty descriptor array is marked as a root before any maps are marked. ASSERT(descriptors != Heap::raw_unchecked_empty_descriptor_array()); SetMark(descriptors); FixedArray* contents = reinterpret_cast( descriptors->get(DescriptorArray::kContentArrayIndex)); ASSERT(contents->IsHeapObject()); ASSERT(!contents->IsMarked()); ASSERT(contents->IsFixedArray()); ASSERT(contents->length() >= 2); SetMark(contents); // Contents contains (value, details) pairs. If the details say // that the type of descriptor is MAP_TRANSITION, CONSTANT_TRANSITION, // or NULL_DESCRIPTOR, we don't mark the value as live. Only for // type MAP_TRANSITION is the value a Object* (a Map*). for (int i = 0; i < contents->length(); i += 2) { // If the pair (value, details) at index i, i+1 is not // a transition or null descriptor, mark the value. PropertyDetails details(Smi::cast(contents->get(i + 1))); if (details.type() < FIRST_PHANTOM_PROPERTY_TYPE) { HeapObject* object = reinterpret_cast(contents->get(i)); if (object->IsHeapObject() && !object->IsMarked()) { SetMark(object); marking_stack.Push(object); } } } // The DescriptorArray descriptors contains a pointer to its contents array, // but the contents array is already marked. marking_stack.Push(descriptors); } void MarkCompactCollector::CreateBackPointers() { HeapObjectIterator iterator(Heap::map_space()); for (HeapObject* next_object = iterator.next(); next_object != NULL; next_object = iterator.next()) { if (next_object->IsMap()) { // Could also be ByteArray on free list. Map* map = Map::cast(next_object); if (map->instance_type() >= FIRST_JS_OBJECT_TYPE && map->instance_type() <= JS_FUNCTION_TYPE) { map->CreateBackPointers(); } else { ASSERT(map->instance_descriptors() == Heap::empty_descriptor_array()); } } } } static int OverflowObjectSize(HeapObject* obj) { // Recover the normal map pointer, it might be marked as live and // overflowed. MapWord map_word = obj->map_word(); map_word.ClearMark(); map_word.ClearOverflow(); return obj->SizeFromMap(map_word.ToMap()); } // Fill the marking stack with overflowed objects returned by the given // iterator. Stop when the marking stack is filled or the end of the space // is reached, whichever comes first. template static void ScanOverflowedObjects(T* it) { // The caller should ensure that the marking stack is initially not full, // so that we don't waste effort pointlessly scanning for objects. ASSERT(!marking_stack.is_full()); for (HeapObject* object = it->next(); object != NULL; object = it->next()) { if (object->IsOverflowed()) { object->ClearOverflow(); ASSERT(object->IsMarked()); ASSERT(Heap::Contains(object)); marking_stack.Push(object); if (marking_stack.is_full()) return; } } } bool MarkCompactCollector::IsUnmarkedHeapObject(Object** p) { return (*p)->IsHeapObject() && !HeapObject::cast(*p)->IsMarked(); } void MarkCompactCollector::MarkSymbolTable() { SymbolTable* symbol_table = Heap::raw_unchecked_symbol_table(); // Mark the symbol table itself. SetMark(symbol_table); // Explicitly mark the prefix. MarkingVisitor marker; symbol_table->IteratePrefix(&marker); ProcessMarkingStack(&marker); } void MarkCompactCollector::MarkRoots(RootMarkingVisitor* visitor) { // Mark the heap roots including global variables, stack variables, // etc., and all objects reachable from them. Heap::IterateStrongRoots(visitor, VISIT_ONLY_STRONG); // Handle the symbol table specially. MarkSymbolTable(); // There may be overflowed objects in the heap. Visit them now. while (marking_stack.overflowed()) { RefillMarkingStack(); EmptyMarkingStack(visitor->stack_visitor()); } } void MarkCompactCollector::MarkObjectGroups() { List* object_groups = GlobalHandles::ObjectGroups(); for (int i = 0; i < object_groups->length(); i++) { ObjectGroup* entry = object_groups->at(i); if (entry == NULL) continue; List& objects = entry->objects_; bool group_marked = false; for (int j = 0; j < objects.length(); j++) { Object* object = *objects[j]; if (object->IsHeapObject() && HeapObject::cast(object)->IsMarked()) { group_marked = true; break; } } if (!group_marked) continue; // An object in the group is marked, so mark as gray all white heap // objects in the group. for (int j = 0; j < objects.length(); ++j) { if ((*objects[j])->IsHeapObject()) { MarkObject(HeapObject::cast(*objects[j])); } } // Once the entire group has been colored gray, set the object group // to NULL so it won't be processed again. delete object_groups->at(i); object_groups->at(i) = NULL; } } // Mark all objects reachable from the objects on the marking stack. // Before: the marking stack contains zero or more heap object pointers. // After: the marking stack is empty, and all objects reachable from the // marking stack have been marked, or are overflowed in the heap. void MarkCompactCollector::EmptyMarkingStack(MarkingVisitor* visitor) { while (!marking_stack.is_empty()) { HeapObject* object = marking_stack.Pop(); ASSERT(object->IsHeapObject()); ASSERT(Heap::Contains(object)); ASSERT(object->IsMarked()); ASSERT(!object->IsOverflowed()); // Because the object is marked, we have to recover the original map // pointer and use it to mark the object's body. MapWord map_word = object->map_word(); map_word.ClearMark(); Map* map = map_word.ToMap(); MarkObject(map); object->IterateBody(map->instance_type(), object->SizeFromMap(map), visitor); } } // Sweep the heap for overflowed objects, clear their overflow bits, and // push them on the marking stack. Stop early if the marking stack fills // before sweeping completes. If sweeping completes, there are no remaining // overflowed objects in the heap so the overflow flag on the markings stack // is cleared. void MarkCompactCollector::RefillMarkingStack() { ASSERT(marking_stack.overflowed()); SemiSpaceIterator new_it(Heap::new_space(), &OverflowObjectSize); ScanOverflowedObjects(&new_it); if (marking_stack.is_full()) return; HeapObjectIterator old_pointer_it(Heap::old_pointer_space(), &OverflowObjectSize); ScanOverflowedObjects(&old_pointer_it); if (marking_stack.is_full()) return; HeapObjectIterator old_data_it(Heap::old_data_space(), &OverflowObjectSize); ScanOverflowedObjects(&old_data_it); if (marking_stack.is_full()) return; HeapObjectIterator code_it(Heap::code_space(), &OverflowObjectSize); ScanOverflowedObjects(&code_it); if (marking_stack.is_full()) return; HeapObjectIterator map_it(Heap::map_space(), &OverflowObjectSize); ScanOverflowedObjects(&map_it); if (marking_stack.is_full()) return; HeapObjectIterator cell_it(Heap::cell_space(), &OverflowObjectSize); ScanOverflowedObjects(&cell_it); if (marking_stack.is_full()) return; LargeObjectIterator lo_it(Heap::lo_space(), &OverflowObjectSize); ScanOverflowedObjects(&lo_it); if (marking_stack.is_full()) return; marking_stack.clear_overflowed(); } // Mark all objects reachable (transitively) from objects on the marking // stack. Before: the marking stack contains zero or more heap object // pointers. After: the marking stack is empty and there are no overflowed // objects in the heap. void MarkCompactCollector::ProcessMarkingStack(MarkingVisitor* visitor) { EmptyMarkingStack(visitor); while (marking_stack.overflowed()) { RefillMarkingStack(); EmptyMarkingStack(visitor); } } void MarkCompactCollector::ProcessObjectGroups(MarkingVisitor* visitor) { bool work_to_do = true; ASSERT(marking_stack.is_empty()); while (work_to_do) { MarkObjectGroups(); work_to_do = !marking_stack.is_empty(); ProcessMarkingStack(visitor); } } void MarkCompactCollector::MarkLiveObjects() { GCTracer::Scope gc_scope(tracer_, GCTracer::Scope::MC_MARK); #ifdef DEBUG ASSERT(state_ == PREPARE_GC); state_ = MARK_LIVE_OBJECTS; #endif // The to space contains live objects, the from space is used as a marking // stack. marking_stack.Initialize(Heap::new_space()->FromSpaceLow(), Heap::new_space()->FromSpaceHigh()); ASSERT(!marking_stack.overflowed()); RootMarkingVisitor root_visitor; MarkRoots(&root_visitor); // The objects reachable from the roots are marked, yet unreachable // objects are unmarked. Mark objects reachable from object groups // containing at least one marked object, and continue until no new // objects are reachable from the object groups. ProcessObjectGroups(root_visitor.stack_visitor()); // The objects reachable from the roots or object groups are marked, // yet unreachable objects are unmarked. Mark objects reachable // only from weak global handles. // // First we identify nonlive weak handles and mark them as pending // destruction. GlobalHandles::IdentifyWeakHandles(&IsUnmarkedHeapObject); // Then we mark the objects and process the transitive closure. GlobalHandles::IterateWeakRoots(&root_visitor); while (marking_stack.overflowed()) { RefillMarkingStack(); EmptyMarkingStack(root_visitor.stack_visitor()); } // Repeat the object groups to mark unmarked groups reachable from the // weak roots. ProcessObjectGroups(root_visitor.stack_visitor()); // Prune the symbol table removing all symbols only pointed to by the // symbol table. Cannot use symbol_table() here because the symbol // table is marked. SymbolTable* symbol_table = Heap::raw_unchecked_symbol_table(); SymbolTableCleaner v; symbol_table->IterateElements(&v); symbol_table->ElementsRemoved(v.PointersRemoved()); ExternalStringTable::Iterate(&v); ExternalStringTable::CleanUp(); // Remove object groups after marking phase. GlobalHandles::RemoveObjectGroups(); } static int CountMarkedCallback(HeapObject* obj) { MapWord map_word = obj->map_word(); map_word.ClearMark(); return obj->SizeFromMap(map_word.ToMap()); } #ifdef DEBUG void MarkCompactCollector::UpdateLiveObjectCount(HeapObject* obj) { live_bytes_ += obj->Size(); if (Heap::new_space()->Contains(obj)) { live_young_objects_size_ += obj->Size(); } else if (Heap::map_space()->Contains(obj)) { ASSERT(obj->IsMap()); live_map_objects_size_ += obj->Size(); } else if (Heap::cell_space()->Contains(obj)) { ASSERT(obj->IsJSGlobalPropertyCell()); live_cell_objects_size_ += obj->Size(); } else if (Heap::old_pointer_space()->Contains(obj)) { live_old_pointer_objects_size_ += obj->Size(); } else if (Heap::old_data_space()->Contains(obj)) { live_old_data_objects_size_ += obj->Size(); } else if (Heap::code_space()->Contains(obj)) { live_code_objects_size_ += obj->Size(); } else if (Heap::lo_space()->Contains(obj)) { live_lo_objects_size_ += obj->Size(); } else { UNREACHABLE(); } } #endif // DEBUG void MarkCompactCollector::SweepLargeObjectSpace() { #ifdef DEBUG ASSERT(state_ == MARK_LIVE_OBJECTS); state_ = compacting_collection_ ? ENCODE_FORWARDING_ADDRESSES : SWEEP_SPACES; #endif // Deallocate unmarked objects and clear marked bits for marked objects. Heap::lo_space()->FreeUnmarkedObjects(); } // Safe to use during marking phase only. bool MarkCompactCollector::SafeIsMap(HeapObject* object) { MapWord metamap = object->map_word(); metamap.ClearMark(); return metamap.ToMap()->instance_type() == MAP_TYPE; } void MarkCompactCollector::ClearNonLiveTransitions() { HeapObjectIterator map_iterator(Heap::map_space(), &CountMarkedCallback); // Iterate over the map space, setting map transitions that go from // a marked map to an unmarked map to null transitions. At the same time, // set all the prototype fields of maps back to their original value, // dropping the back pointers temporarily stored in the prototype field. // Setting the prototype field requires following the linked list of // back pointers, reversing them all at once. This allows us to find // those maps with map transitions that need to be nulled, and only // scan the descriptor arrays of those maps, not all maps. // All of these actions are carried out only on maps of JSObjects // and related subtypes. for (HeapObject* obj = map_iterator.next(); obj != NULL; obj = map_iterator.next()) { Map* map = reinterpret_cast(obj); if (!map->IsMarked() && map->IsByteArray()) continue; ASSERT(SafeIsMap(map)); // Only JSObject and subtypes have map transitions and back pointers. if (map->instance_type() < FIRST_JS_OBJECT_TYPE) continue; if (map->instance_type() > JS_FUNCTION_TYPE) continue; // Follow the chain of back pointers to find the prototype. Map* current = map; while (SafeIsMap(current)) { current = reinterpret_cast(current->prototype()); ASSERT(current->IsHeapObject()); } Object* real_prototype = current; // Follow back pointers, setting them to prototype, // clearing map transitions when necessary. current = map; bool on_dead_path = !current->IsMarked(); Object* next; while (SafeIsMap(current)) { next = current->prototype(); // There should never be a dead map above a live map. ASSERT(on_dead_path || current->IsMarked()); // A live map above a dead map indicates a dead transition. // This test will always be false on the first iteration. if (on_dead_path && current->IsMarked()) { on_dead_path = false; current->ClearNonLiveTransitions(real_prototype); } *HeapObject::RawField(current, Map::kPrototypeOffset) = real_prototype; current = reinterpret_cast(next); } } } // ------------------------------------------------------------------------- // Phase 2: Encode forwarding addresses. // When compacting, forwarding addresses for objects in old space and map // space are encoded in their map pointer word (along with an encoding of // their map pointers). // // The excact encoding is described in the comments for class MapWord in // objects.h. // // An address range [start, end) can have both live and non-live objects. // Maximal non-live regions are marked so they can be skipped on subsequent // sweeps of the heap. A distinguished map-pointer encoding is used to mark // free regions of one-word size (in which case the next word is the start // of a live object). A second distinguished map-pointer encoding is used // to mark free regions larger than one word, and the size of the free // region (including the first word) is written to the second word of the // region. // // Any valid map page offset must lie in the object area of the page, so map // page offsets less than Page::kObjectStartOffset are invalid. We use a // pair of distinguished invalid map encodings (for single word and multiple // words) to indicate free regions in the page found during computation of // forwarding addresses and skipped over in subsequent sweeps. static const uint32_t kSingleFreeEncoding = 0; static const uint32_t kMultiFreeEncoding = 1; // Encode a free region, defined by the given start address and size, in the // first word or two of the region. void EncodeFreeRegion(Address free_start, int free_size) { ASSERT(free_size >= kIntSize); if (free_size == kIntSize) { Memory::uint32_at(free_start) = kSingleFreeEncoding; } else { ASSERT(free_size >= 2 * kIntSize); Memory::uint32_at(free_start) = kMultiFreeEncoding; Memory::int_at(free_start + kIntSize) = free_size; } #ifdef DEBUG // Zap the body of the free region. if (FLAG_enable_slow_asserts) { for (int offset = 2 * kIntSize; offset < free_size; offset += kPointerSize) { Memory::Address_at(free_start + offset) = kZapValue; } } #endif } // Try to promote all objects in new space. Heap numbers and sequential // strings are promoted to the code space, large objects to large object space, // and all others to the old space. inline Object* MCAllocateFromNewSpace(HeapObject* object, int object_size) { Object* forwarded; if (object_size > Heap::MaxObjectSizeInPagedSpace()) { forwarded = Failure::Exception(); } else { OldSpace* target_space = Heap::TargetSpace(object); ASSERT(target_space == Heap::old_pointer_space() || target_space == Heap::old_data_space()); forwarded = target_space->MCAllocateRaw(object_size); } if (forwarded->IsFailure()) { forwarded = Heap::new_space()->MCAllocateRaw(object_size); } return forwarded; } // Allocation functions for the paged spaces call the space's MCAllocateRaw. inline Object* MCAllocateFromOldPointerSpace(HeapObject* ignore, int object_size) { return Heap::old_pointer_space()->MCAllocateRaw(object_size); } inline Object* MCAllocateFromOldDataSpace(HeapObject* ignore, int object_size) { return Heap::old_data_space()->MCAllocateRaw(object_size); } inline Object* MCAllocateFromCodeSpace(HeapObject* ignore, int object_size) { return Heap::code_space()->MCAllocateRaw(object_size); } inline Object* MCAllocateFromMapSpace(HeapObject* ignore, int object_size) { return Heap::map_space()->MCAllocateRaw(object_size); } inline Object* MCAllocateFromCellSpace(HeapObject* ignore, int object_size) { return Heap::cell_space()->MCAllocateRaw(object_size); } // The forwarding address is encoded at the same offset as the current // to-space object, but in from space. inline void EncodeForwardingAddressInNewSpace(HeapObject* old_object, int object_size, Object* new_object, int* ignored) { int offset = Heap::new_space()->ToSpaceOffsetForAddress(old_object->address()); Memory::Address_at(Heap::new_space()->FromSpaceLow() + offset) = HeapObject::cast(new_object)->address(); } // The forwarding address is encoded in the map pointer of the object as an // offset (in terms of live bytes) from the address of the first live object // in the page. inline void EncodeForwardingAddressInPagedSpace(HeapObject* old_object, int object_size, Object* new_object, int* offset) { // Record the forwarding address of the first live object if necessary. if (*offset == 0) { Page::FromAddress(old_object->address())->mc_first_forwarded = HeapObject::cast(new_object)->address(); } MapWord encoding = MapWord::EncodeAddress(old_object->map()->address(), *offset); old_object->set_map_word(encoding); *offset += object_size; ASSERT(*offset <= Page::kObjectAreaSize); } // Most non-live objects are ignored. inline void IgnoreNonLiveObject(HeapObject* object) {} // Function template that, given a range of addresses (eg, a semispace or a // paged space page), iterates through the objects in the range to clear // mark bits and compute and encode forwarding addresses. As a side effect, // maximal free chunks are marked so that they can be skipped on subsequent // sweeps. // // The template parameters are an allocation function, a forwarding address // encoding function, and a function to process non-live objects. template inline void EncodeForwardingAddressesInRange(Address start, Address end, int* offset) { // The start address of the current free region while sweeping the space. // This address is set when a transition from live to non-live objects is // encountered. A value (an encoding of the 'next free region' pointer) // is written to memory at this address when a transition from non-live to // live objects is encountered. Address free_start = NULL; // A flag giving the state of the previously swept object. Initially true // to ensure that free_start is initialized to a proper address before // trying to write to it. bool is_prev_alive = true; int object_size; // Will be set on each iteration of the loop. for (Address current = start; current < end; current += object_size) { HeapObject* object = HeapObject::FromAddress(current); if (object->IsMarked()) { object->ClearMark(); MarkCompactCollector::tracer()->decrement_marked_count(); object_size = object->Size(); Object* forwarded = Alloc(object, object_size); // Allocation cannot fail, because we are compacting the space. ASSERT(!forwarded->IsFailure()); Encode(object, object_size, forwarded, offset); #ifdef DEBUG if (FLAG_gc_verbose) { PrintF("forward %p -> %p.\n", object->address(), HeapObject::cast(forwarded)->address()); } #endif if (!is_prev_alive) { // Transition from non-live to live. EncodeFreeRegion(free_start, static_cast(current - free_start)); is_prev_alive = true; } } else { // Non-live object. object_size = object->Size(); ProcessNonLive(object); if (is_prev_alive) { // Transition from live to non-live. free_start = current; is_prev_alive = false; } } } // If we ended on a free region, mark it. if (!is_prev_alive) { EncodeFreeRegion(free_start, static_cast(end - free_start)); } } // Functions to encode the forwarding pointers in each compactable space. void MarkCompactCollector::EncodeForwardingAddressesInNewSpace() { int ignored; EncodeForwardingAddressesInRange( Heap::new_space()->bottom(), Heap::new_space()->top(), &ignored); } template void MarkCompactCollector::EncodeForwardingAddressesInPagedSpace( PagedSpace* space) { PageIterator it(space, PageIterator::PAGES_IN_USE); while (it.has_next()) { Page* p = it.next(); // The offset of each live object in the page from the first live object // in the page. int offset = 0; EncodeForwardingAddressesInRange( p->ObjectAreaStart(), p->AllocationTop(), &offset); } } // We scavange new space simultaneously with sweeping. This is done in two // passes. // The first pass migrates all alive objects from one semispace to another or // promotes them to old space. Forwading address is written directly into // first word of object without any encoding. If object is dead we are writing // NULL as a forwarding address. // The second pass updates pointers to new space in all spaces. It is possible // to encounter pointers to dead objects during traversal of dirty regions we // should clear them to avoid encountering them during next dirty regions // iteration. static void MigrateObject(Address dst, Address src, int size, bool to_old_space) { if (to_old_space) { Heap::CopyBlockToOldSpaceAndUpdateRegionMarks(dst, src, size); } else { Heap::CopyBlock(dst, src, size); } Memory::Address_at(src) = dst; } // Visitor for updating pointers from live objects in old spaces to new space. // It does not expect to encounter pointers to dead objects. class PointersToNewGenUpdatingVisitor: public ObjectVisitor { public: void VisitPointer(Object** p) { UpdatePointer(p); } void VisitPointers(Object** start, Object** end) { for (Object** p = start; p < end; p++) UpdatePointer(p); } void VisitCodeTarget(RelocInfo* rinfo) { ASSERT(RelocInfo::IsCodeTarget(rinfo->rmode())); Object* target = Code::GetCodeFromTargetAddress(rinfo->target_address()); VisitPointer(&target); rinfo->set_target_address(Code::cast(target)->instruction_start()); } void VisitDebugTarget(RelocInfo* rinfo) { ASSERT((RelocInfo::IsJSReturn(rinfo->rmode()) && rinfo->IsPatchedReturnSequence()) || (RelocInfo::IsDebugBreakSlot(rinfo->rmode()) && rinfo->IsPatchedDebugBreakSlotSequence())); Object* target = Code::GetCodeFromTargetAddress(rinfo->call_address()); VisitPointer(&target); rinfo->set_call_address(Code::cast(target)->instruction_start()); } private: void UpdatePointer(Object** p) { if (!(*p)->IsHeapObject()) return; HeapObject* obj = HeapObject::cast(*p); Address old_addr = obj->address(); if (Heap::new_space()->Contains(obj)) { ASSERT(Heap::InFromSpace(*p)); *p = HeapObject::FromAddress(Memory::Address_at(old_addr)); } } }; // Visitor for updating pointers from live objects in old spaces to new space. // It can encounter pointers to dead objects in new space when traversing map // space (see comment for MigrateObject). static void UpdatePointerToNewGen(HeapObject** p) { if (!(*p)->IsHeapObject()) return; Address old_addr = (*p)->address(); ASSERT(Heap::InFromSpace(*p)); Address new_addr = Memory::Address_at(old_addr); if (new_addr == NULL) { // We encountered pointer to a dead object. Clear it so we will // not visit it again during next iteration of dirty regions. *p = NULL; } else { *p = HeapObject::FromAddress(new_addr); } } static String* UpdateNewSpaceReferenceInExternalStringTableEntry(Object **p) { Address old_addr = HeapObject::cast(*p)->address(); Address new_addr = Memory::Address_at(old_addr); return String::cast(HeapObject::FromAddress(new_addr)); } static bool TryPromoteObject(HeapObject* object, int object_size) { Object* result; if (object_size > Heap::MaxObjectSizeInPagedSpace()) { result = Heap::lo_space()->AllocateRawFixedArray(object_size); if (!result->IsFailure()) { HeapObject* target = HeapObject::cast(result); MigrateObject(target->address(), object->address(), object_size, true); MarkCompactCollector::tracer()-> increment_promoted_objects_size(object_size); return true; } } else { OldSpace* target_space = Heap::TargetSpace(object); ASSERT(target_space == Heap::old_pointer_space() || target_space == Heap::old_data_space()); result = target_space->AllocateRaw(object_size); if (!result->IsFailure()) { HeapObject* target = HeapObject::cast(result); MigrateObject(target->address(), object->address(), object_size, target_space == Heap::old_pointer_space()); MarkCompactCollector::tracer()-> increment_promoted_objects_size(object_size); return true; } } return false; } static void SweepNewSpace(NewSpace* space) { Heap::CheckNewSpaceExpansionCriteria(); Address from_bottom = space->bottom(); Address from_top = space->top(); // Flip the semispaces. After flipping, to space is empty, from space has // live objects. space->Flip(); space->ResetAllocationInfo(); int size = 0; int survivors_size = 0; // First pass: traverse all objects in inactive semispace, remove marks, // migrate live objects and write forwarding addresses. for (Address current = from_bottom; current < from_top; current += size) { HeapObject* object = HeapObject::FromAddress(current); if (object->IsMarked()) { object->ClearMark(); MarkCompactCollector::tracer()->decrement_marked_count(); size = object->Size(); survivors_size += size; // Aggressively promote young survivors to the old space. if (TryPromoteObject(object, size)) { continue; } // Promotion failed. Just migrate object to another semispace. Object* target = space->AllocateRaw(size); // Allocation cannot fail at this point: semispaces are of equal size. ASSERT(!target->IsFailure()); MigrateObject(HeapObject::cast(target)->address(), current, size, false); } else { size = object->Size(); Memory::Address_at(current) = NULL; } } // Second pass: find pointers to new space and update them. PointersToNewGenUpdatingVisitor updating_visitor; // Update pointers in to space. HeapObject* object; for (Address current = space->bottom(); current < space->top(); current += object->Size()) { object = HeapObject::FromAddress(current); object->IterateBody(object->map()->instance_type(), object->Size(), &updating_visitor); } // Update roots. Heap::IterateRoots(&updating_visitor, VISIT_ALL_IN_SCAVENGE); // Update pointers in old spaces. Heap::IterateDirtyRegions(Heap::old_pointer_space(), &Heap::IteratePointersInDirtyRegion, &UpdatePointerToNewGen, Heap::WATERMARK_SHOULD_BE_VALID); Heap::lo_space()->IterateDirtyRegions(&UpdatePointerToNewGen); // Update pointers from cells. HeapObjectIterator cell_iterator(Heap::cell_space()); for (HeapObject* cell = cell_iterator.next(); cell != NULL; cell = cell_iterator.next()) { if (cell->IsJSGlobalPropertyCell()) { Address value_address = reinterpret_cast
(cell) + (JSGlobalPropertyCell::kValueOffset - kHeapObjectTag); updating_visitor.VisitPointer(reinterpret_cast(value_address)); } } // Update pointers from external string table. Heap::UpdateNewSpaceReferencesInExternalStringTable( &UpdateNewSpaceReferenceInExternalStringTableEntry); // All pointers were updated. Update auxiliary allocation info. Heap::IncrementYoungSurvivorsCounter(survivors_size); space->set_age_mark(space->top()); } static void SweepSpace(PagedSpace* space, DeallocateFunction dealloc) { PageIterator it(space, PageIterator::PAGES_IN_USE); // During sweeping of paged space we are trying to find longest sequences // of pages without live objects and free them (instead of putting them on // the free list). // Page preceding current. Page* prev = Page::FromAddress(NULL); // First empty page in a sequence. Page* first_empty_page = Page::FromAddress(NULL); // Page preceding first empty page. Page* prec_first_empty_page = Page::FromAddress(NULL); // If last used page of space ends with a sequence of dead objects // we can adjust allocation top instead of puting this free area into // the free list. Thus during sweeping we keep track of such areas // and defer their deallocation until the sweeping of the next page // is done: if one of the next pages contains live objects we have // to put such area into the free list. Address last_free_start = NULL; int last_free_size = 0; while (it.has_next()) { Page* p = it.next(); bool is_previous_alive = true; Address free_start = NULL; HeapObject* object; for (Address current = p->ObjectAreaStart(); current < p->AllocationTop(); current += object->Size()) { object = HeapObject::FromAddress(current); if (object->IsMarked()) { object->ClearMark(); MarkCompactCollector::tracer()->decrement_marked_count(); if (!is_previous_alive) { // Transition from free to live. dealloc(free_start, static_cast(current - free_start), true, false); is_previous_alive = true; } } else { MarkCompactCollector::ReportDeleteIfNeeded(object); if (is_previous_alive) { // Transition from live to free. free_start = current; is_previous_alive = false; } } // The object is now unmarked for the call to Size() at the top of the // loop. } bool page_is_empty = (p->ObjectAreaStart() == p->AllocationTop()) || (!is_previous_alive && free_start == p->ObjectAreaStart()); if (page_is_empty) { // This page is empty. Check whether we are in the middle of // sequence of empty pages and start one if not. if (!first_empty_page->is_valid()) { first_empty_page = p; prec_first_empty_page = prev; } if (!is_previous_alive) { // There are dead objects on this page. Update space accounting stats // without putting anything into free list. int size_in_bytes = static_cast(p->AllocationTop() - free_start); if (size_in_bytes > 0) { dealloc(free_start, size_in_bytes, false, true); } } } else { // This page is not empty. Sequence of empty pages ended on the previous // one. if (first_empty_page->is_valid()) { space->FreePages(prec_first_empty_page, prev); prec_first_empty_page = first_empty_page = Page::FromAddress(NULL); } // If there is a free ending area on one of the previous pages we have // deallocate that area and put it on the free list. if (last_free_size > 0) { Page::FromAddress(last_free_start)-> SetAllocationWatermark(last_free_start); dealloc(last_free_start, last_free_size, true, true); last_free_start = NULL; last_free_size = 0; } // If the last region of this page was not live we remember it. if (!is_previous_alive) { ASSERT(last_free_size == 0); last_free_size = static_cast(p->AllocationTop() - free_start); last_free_start = free_start; } } prev = p; } // We reached end of space. See if we need to adjust allocation top. Address new_allocation_top = NULL; if (first_empty_page->is_valid()) { // Last used pages in space are empty. We can move allocation top backwards // to the beginning of first empty page. ASSERT(prev == space->AllocationTopPage()); new_allocation_top = first_empty_page->ObjectAreaStart(); } if (last_free_size > 0) { // There was a free ending area on the previous page. // Deallocate it without putting it into freelist and move allocation // top to the beginning of this free area. dealloc(last_free_start, last_free_size, false, true); new_allocation_top = last_free_start; } if (new_allocation_top != NULL) { #ifdef DEBUG Page* new_allocation_top_page = Page::FromAllocationTop(new_allocation_top); if (!first_empty_page->is_valid()) { ASSERT(new_allocation_top_page == space->AllocationTopPage()); } else if (last_free_size > 0) { ASSERT(new_allocation_top_page == prec_first_empty_page); } else { ASSERT(new_allocation_top_page == first_empty_page); } #endif space->SetTop(new_allocation_top); } } void MarkCompactCollector::DeallocateOldPointerBlock(Address start, int size_in_bytes, bool add_to_freelist, bool last_on_page) { Heap::old_pointer_space()->Free(start, size_in_bytes, add_to_freelist); } void MarkCompactCollector::DeallocateOldDataBlock(Address start, int size_in_bytes, bool add_to_freelist, bool last_on_page) { Heap::old_data_space()->Free(start, size_in_bytes, add_to_freelist); } void MarkCompactCollector::DeallocateCodeBlock(Address start, int size_in_bytes, bool add_to_freelist, bool last_on_page) { Heap::code_space()->Free(start, size_in_bytes, add_to_freelist); } void MarkCompactCollector::DeallocateMapBlock(Address start, int size_in_bytes, bool add_to_freelist, bool last_on_page) { // Objects in map space are assumed to have size Map::kSize and a // valid map in their first word. Thus, we break the free block up into // chunks and free them separately. ASSERT(size_in_bytes % Map::kSize == 0); Address end = start + size_in_bytes; for (Address a = start; a < end; a += Map::kSize) { Heap::map_space()->Free(a, add_to_freelist); } } void MarkCompactCollector::DeallocateCellBlock(Address start, int size_in_bytes, bool add_to_freelist, bool last_on_page) { // Free-list elements in cell space are assumed to have a fixed size. // We break the free block into chunks and add them to the free list // individually. int size = Heap::cell_space()->object_size_in_bytes(); ASSERT(size_in_bytes % size == 0); Address end = start + size_in_bytes; for (Address a = start; a < end; a += size) { Heap::cell_space()->Free(a, add_to_freelist); } } void MarkCompactCollector::EncodeForwardingAddresses() { ASSERT(state_ == ENCODE_FORWARDING_ADDRESSES); // Objects in the active semispace of the young generation may be // relocated to the inactive semispace (if not promoted). Set the // relocation info to the beginning of the inactive semispace. Heap::new_space()->MCResetRelocationInfo(); // Compute the forwarding pointers in each space. EncodeForwardingAddressesInPagedSpace( Heap::old_pointer_space()); EncodeForwardingAddressesInPagedSpace( Heap::old_data_space()); EncodeForwardingAddressesInPagedSpace( Heap::code_space()); EncodeForwardingAddressesInPagedSpace( Heap::cell_space()); // Compute new space next to last after the old and code spaces have been // compacted. Objects in new space can be promoted to old or code space. EncodeForwardingAddressesInNewSpace(); // Compute map space last because computing forwarding addresses // overwrites non-live objects. Objects in the other spaces rely on // non-live map pointers to get the sizes of non-live objects. EncodeForwardingAddressesInPagedSpace( Heap::map_space()); // Write relocation info to the top page, so we can use it later. This is // done after promoting objects from the new space so we get the correct // allocation top. Heap::old_pointer_space()->MCWriteRelocationInfoToPage(); Heap::old_data_space()->MCWriteRelocationInfoToPage(); Heap::code_space()->MCWriteRelocationInfoToPage(); Heap::map_space()->MCWriteRelocationInfoToPage(); Heap::cell_space()->MCWriteRelocationInfoToPage(); } class MapIterator : public HeapObjectIterator { public: MapIterator() : HeapObjectIterator(Heap::map_space(), &SizeCallback) { } explicit MapIterator(Address start) : HeapObjectIterator(Heap::map_space(), start, &SizeCallback) { } private: static int SizeCallback(HeapObject* unused) { USE(unused); return Map::kSize; } }; class MapCompact { public: explicit MapCompact(int live_maps) : live_maps_(live_maps), to_evacuate_start_(Heap::map_space()->TopAfterCompaction(live_maps)), map_to_evacuate_it_(to_evacuate_start_), first_map_to_evacuate_( reinterpret_cast(HeapObject::FromAddress(to_evacuate_start_))) { } void CompactMaps() { // As we know the number of maps to evacuate beforehand, // we stop then there is no more vacant maps. for (Map* next_vacant_map = NextVacantMap(); next_vacant_map; next_vacant_map = NextVacantMap()) { EvacuateMap(next_vacant_map, NextMapToEvacuate()); } #ifdef DEBUG CheckNoMapsToEvacuate(); #endif } void UpdateMapPointersInRoots() { Heap::IterateRoots(&map_updating_visitor_, VISIT_ONLY_STRONG); GlobalHandles::IterateWeakRoots(&map_updating_visitor_); } void UpdateMapPointersInPagedSpace(PagedSpace* space) { ASSERT(space != Heap::map_space()); PageIterator it(space, PageIterator::PAGES_IN_USE); while (it.has_next()) { Page* p = it.next(); UpdateMapPointersInRange(p->ObjectAreaStart(), p->AllocationTop()); } } void UpdateMapPointersInNewSpace() { NewSpace* space = Heap::new_space(); UpdateMapPointersInRange(space->bottom(), space->top()); } void UpdateMapPointersInLargeObjectSpace() { LargeObjectIterator it(Heap::lo_space()); for (HeapObject* obj = it.next(); obj != NULL; obj = it.next()) UpdateMapPointersInObject(obj); } void Finish() { Heap::map_space()->FinishCompaction(to_evacuate_start_, live_maps_); } private: int live_maps_; Address to_evacuate_start_; MapIterator vacant_map_it_; MapIterator map_to_evacuate_it_; Map* first_map_to_evacuate_; // Helper class for updating map pointers in HeapObjects. class MapUpdatingVisitor: public ObjectVisitor { public: void VisitPointer(Object** p) { UpdateMapPointer(p); } void VisitPointers(Object** start, Object** end) { for (Object** p = start; p < end; p++) UpdateMapPointer(p); } private: void UpdateMapPointer(Object** p) { if (!(*p)->IsHeapObject()) return; HeapObject* old_map = reinterpret_cast(*p); // Moved maps are tagged with overflowed map word. They are the only // objects those map word is overflowed as marking is already complete. MapWord map_word = old_map->map_word(); if (!map_word.IsOverflowed()) return; *p = GetForwardedMap(map_word); } }; static MapUpdatingVisitor map_updating_visitor_; static Map* NextMap(MapIterator* it, HeapObject* last, bool live) { while (true) { HeapObject* next = it->next(); ASSERT(next != NULL); if (next == last) return NULL; ASSERT(!next->IsOverflowed()); ASSERT(!next->IsMarked()); ASSERT(next->IsMap() || FreeListNode::IsFreeListNode(next)); if (next->IsMap() == live) return reinterpret_cast(next); } } Map* NextVacantMap() { Map* map = NextMap(&vacant_map_it_, first_map_to_evacuate_, false); ASSERT(map == NULL || FreeListNode::IsFreeListNode(map)); return map; } Map* NextMapToEvacuate() { Map* map = NextMap(&map_to_evacuate_it_, NULL, true); ASSERT(map != NULL); ASSERT(map->IsMap()); return map; } static void EvacuateMap(Map* vacant_map, Map* map_to_evacuate) { ASSERT(FreeListNode::IsFreeListNode(vacant_map)); ASSERT(map_to_evacuate->IsMap()); ASSERT(Map::kSize % 4 == 0); Heap::CopyBlockToOldSpaceAndUpdateRegionMarks(vacant_map->address(), map_to_evacuate->address(), Map::kSize); ASSERT(vacant_map->IsMap()); // Due to memcpy above. MapWord forwarding_map_word = MapWord::FromMap(vacant_map); forwarding_map_word.SetOverflow(); map_to_evacuate->set_map_word(forwarding_map_word); ASSERT(map_to_evacuate->map_word().IsOverflowed()); ASSERT(GetForwardedMap(map_to_evacuate->map_word()) == vacant_map); } static Map* GetForwardedMap(MapWord map_word) { ASSERT(map_word.IsOverflowed()); map_word.ClearOverflow(); Map* new_map = map_word.ToMap(); ASSERT_MAP_ALIGNED(new_map->address()); return new_map; } static int UpdateMapPointersInObject(HeapObject* obj) { ASSERT(!obj->IsMarked()); Map* map = obj->map(); ASSERT(Heap::map_space()->Contains(map)); MapWord map_word = map->map_word(); ASSERT(!map_word.IsMarked()); if (map_word.IsOverflowed()) { Map* new_map = GetForwardedMap(map_word); ASSERT(Heap::map_space()->Contains(new_map)); obj->set_map(new_map); #ifdef DEBUG if (FLAG_gc_verbose) { PrintF("update %p : %p -> %p\n", obj->address(), map, new_map); } #endif } int size = obj->SizeFromMap(map); obj->IterateBody(map->instance_type(), size, &map_updating_visitor_); return size; } static void UpdateMapPointersInRange(Address start, Address end) { HeapObject* object; int size; for (Address current = start; current < end; current += size) { object = HeapObject::FromAddress(current); size = UpdateMapPointersInObject(object); ASSERT(size > 0); } } #ifdef DEBUG void CheckNoMapsToEvacuate() { if (!FLAG_enable_slow_asserts) return; for (HeapObject* obj = map_to_evacuate_it_.next(); obj != NULL; obj = map_to_evacuate_it_.next()) ASSERT(FreeListNode::IsFreeListNode(obj)); } #endif }; MapCompact::MapUpdatingVisitor MapCompact::map_updating_visitor_; void MarkCompactCollector::SweepSpaces() { GCTracer::Scope gc_scope(tracer_, GCTracer::Scope::MC_SWEEP); ASSERT(state_ == SWEEP_SPACES); ASSERT(!IsCompacting()); // Noncompacting collections simply sweep the spaces to clear the mark // bits and free the nonlive blocks (for old and map spaces). We sweep // the map space last because freeing non-live maps overwrites them and // the other spaces rely on possibly non-live maps to get the sizes for // non-live objects. SweepSpace(Heap::old_pointer_space(), &DeallocateOldPointerBlock); SweepSpace(Heap::old_data_space(), &DeallocateOldDataBlock); SweepSpace(Heap::code_space(), &DeallocateCodeBlock); SweepSpace(Heap::cell_space(), &DeallocateCellBlock); SweepNewSpace(Heap::new_space()); SweepSpace(Heap::map_space(), &DeallocateMapBlock); Heap::IterateDirtyRegions(Heap::map_space(), &Heap::IteratePointersInDirtyMapsRegion, &UpdatePointerToNewGen, Heap::WATERMARK_SHOULD_BE_VALID); int live_maps_size = Heap::map_space()->Size(); int live_maps = live_maps_size / Map::kSize; ASSERT(live_map_objects_size_ == live_maps_size); if (Heap::map_space()->NeedsCompaction(live_maps)) { MapCompact map_compact(live_maps); map_compact.CompactMaps(); map_compact.UpdateMapPointersInRoots(); PagedSpaces spaces; for (PagedSpace* space = spaces.next(); space != NULL; space = spaces.next()) { if (space == Heap::map_space()) continue; map_compact.UpdateMapPointersInPagedSpace(space); } map_compact.UpdateMapPointersInNewSpace(); map_compact.UpdateMapPointersInLargeObjectSpace(); map_compact.Finish(); } } // Iterate the live objects in a range of addresses (eg, a page or a // semispace). The live regions of the range have been linked into a list. // The first live region is [first_live_start, first_live_end), and the last // address in the range is top. The callback function is used to get the // size of each live object. int MarkCompactCollector::IterateLiveObjectsInRange( Address start, Address end, HeapObjectCallback size_func) { int live_objects_size = 0; Address current = start; while (current < end) { uint32_t encoded_map = Memory::uint32_at(current); if (encoded_map == kSingleFreeEncoding) { current += kPointerSize; } else if (encoded_map == kMultiFreeEncoding) { current += Memory::int_at(current + kIntSize); } else { int size = size_func(HeapObject::FromAddress(current)); current += size; live_objects_size += size; } } return live_objects_size; } int MarkCompactCollector::IterateLiveObjects(NewSpace* space, HeapObjectCallback size_f) { ASSERT(MARK_LIVE_OBJECTS < state_ && state_ <= RELOCATE_OBJECTS); return IterateLiveObjectsInRange(space->bottom(), space->top(), size_f); } int MarkCompactCollector::IterateLiveObjects(PagedSpace* space, HeapObjectCallback size_f) { ASSERT(MARK_LIVE_OBJECTS < state_ && state_ <= RELOCATE_OBJECTS); int total = 0; PageIterator it(space, PageIterator::PAGES_IN_USE); while (it.has_next()) { Page* p = it.next(); total += IterateLiveObjectsInRange(p->ObjectAreaStart(), p->AllocationTop(), size_f); } return total; } // ------------------------------------------------------------------------- // Phase 3: Update pointers // Helper class for updating pointers in HeapObjects. class UpdatingVisitor: public ObjectVisitor { public: void VisitPointer(Object** p) { UpdatePointer(p); } void VisitPointers(Object** start, Object** end) { // Mark all HeapObject pointers in [start, end) for (Object** p = start; p < end; p++) UpdatePointer(p); } void VisitCodeTarget(RelocInfo* rinfo) { ASSERT(RelocInfo::IsCodeTarget(rinfo->rmode())); Object* target = Code::GetCodeFromTargetAddress(rinfo->target_address()); VisitPointer(&target); rinfo->set_target_address( reinterpret_cast(target)->instruction_start()); } void VisitDebugTarget(RelocInfo* rinfo) { ASSERT((RelocInfo::IsJSReturn(rinfo->rmode()) && rinfo->IsPatchedReturnSequence()) || (RelocInfo::IsDebugBreakSlot(rinfo->rmode()) && rinfo->IsPatchedDebugBreakSlotSequence())); Object* target = Code::GetCodeFromTargetAddress(rinfo->call_address()); VisitPointer(&target); rinfo->set_call_address( reinterpret_cast(target)->instruction_start()); } private: void UpdatePointer(Object** p) { if (!(*p)->IsHeapObject()) return; HeapObject* obj = HeapObject::cast(*p); Address old_addr = obj->address(); Address new_addr; ASSERT(!Heap::InFromSpace(obj)); if (Heap::new_space()->Contains(obj)) { Address forwarding_pointer_addr = Heap::new_space()->FromSpaceLow() + Heap::new_space()->ToSpaceOffsetForAddress(old_addr); new_addr = Memory::Address_at(forwarding_pointer_addr); #ifdef DEBUG ASSERT(Heap::old_pointer_space()->Contains(new_addr) || Heap::old_data_space()->Contains(new_addr) || Heap::new_space()->FromSpaceContains(new_addr) || Heap::lo_space()->Contains(HeapObject::FromAddress(new_addr))); if (Heap::new_space()->FromSpaceContains(new_addr)) { ASSERT(Heap::new_space()->FromSpaceOffsetForAddress(new_addr) <= Heap::new_space()->ToSpaceOffsetForAddress(old_addr)); } #endif } else if (Heap::lo_space()->Contains(obj)) { // Don't move objects in the large object space. return; } else { #ifdef DEBUG PagedSpaces spaces; PagedSpace* original_space = spaces.next(); while (original_space != NULL) { if (original_space->Contains(obj)) break; original_space = spaces.next(); } ASSERT(original_space != NULL); #endif new_addr = MarkCompactCollector::GetForwardingAddressInOldSpace(obj); ASSERT(original_space->Contains(new_addr)); ASSERT(original_space->MCSpaceOffsetForAddress(new_addr) <= original_space->MCSpaceOffsetForAddress(old_addr)); } *p = HeapObject::FromAddress(new_addr); #ifdef DEBUG if (FLAG_gc_verbose) { PrintF("update %p : %p -> %p\n", reinterpret_cast
(p), old_addr, new_addr); } #endif } }; void MarkCompactCollector::UpdatePointers() { #ifdef DEBUG ASSERT(state_ == ENCODE_FORWARDING_ADDRESSES); state_ = UPDATE_POINTERS; #endif UpdatingVisitor updating_visitor; Heap::IterateRoots(&updating_visitor, VISIT_ONLY_STRONG); GlobalHandles::IterateWeakRoots(&updating_visitor); int live_maps_size = IterateLiveObjects(Heap::map_space(), &UpdatePointersInOldObject); int live_pointer_olds_size = IterateLiveObjects(Heap::old_pointer_space(), &UpdatePointersInOldObject); int live_data_olds_size = IterateLiveObjects(Heap::old_data_space(), &UpdatePointersInOldObject); int live_codes_size = IterateLiveObjects(Heap::code_space(), &UpdatePointersInOldObject); int live_cells_size = IterateLiveObjects(Heap::cell_space(), &UpdatePointersInOldObject); int live_news_size = IterateLiveObjects(Heap::new_space(), &UpdatePointersInNewObject); // Large objects do not move, the map word can be updated directly. LargeObjectIterator it(Heap::lo_space()); for (HeapObject* obj = it.next(); obj != NULL; obj = it.next()) UpdatePointersInNewObject(obj); USE(live_maps_size); USE(live_pointer_olds_size); USE(live_data_olds_size); USE(live_codes_size); USE(live_cells_size); USE(live_news_size); ASSERT(live_maps_size == live_map_objects_size_); ASSERT(live_data_olds_size == live_old_data_objects_size_); ASSERT(live_pointer_olds_size == live_old_pointer_objects_size_); ASSERT(live_codes_size == live_code_objects_size_); ASSERT(live_cells_size == live_cell_objects_size_); ASSERT(live_news_size == live_young_objects_size_); } int MarkCompactCollector::UpdatePointersInNewObject(HeapObject* obj) { // Keep old map pointers Map* old_map = obj->map(); ASSERT(old_map->IsHeapObject()); Address forwarded = GetForwardingAddressInOldSpace(old_map); ASSERT(Heap::map_space()->Contains(old_map)); ASSERT(Heap::map_space()->Contains(forwarded)); #ifdef DEBUG if (FLAG_gc_verbose) { PrintF("update %p : %p -> %p\n", obj->address(), old_map->address(), forwarded); } #endif // Update the map pointer. obj->set_map(reinterpret_cast(HeapObject::FromAddress(forwarded))); // We have to compute the object size relying on the old map because // map objects are not relocated yet. int obj_size = obj->SizeFromMap(old_map); // Update pointers in the object body. UpdatingVisitor updating_visitor; obj->IterateBody(old_map->instance_type(), obj_size, &updating_visitor); return obj_size; } int MarkCompactCollector::UpdatePointersInOldObject(HeapObject* obj) { // Decode the map pointer. MapWord encoding = obj->map_word(); Address map_addr = encoding.DecodeMapAddress(Heap::map_space()); ASSERT(Heap::map_space()->Contains(HeapObject::FromAddress(map_addr))); // At this point, the first word of map_addr is also encoded, cannot // cast it to Map* using Map::cast. Map* map = reinterpret_cast(HeapObject::FromAddress(map_addr)); int obj_size = obj->SizeFromMap(map); InstanceType type = map->instance_type(); // Update map pointer. Address new_map_addr = GetForwardingAddressInOldSpace(map); int offset = encoding.DecodeOffset(); obj->set_map_word(MapWord::EncodeAddress(new_map_addr, offset)); #ifdef DEBUG if (FLAG_gc_verbose) { PrintF("update %p : %p -> %p\n", obj->address(), map_addr, new_map_addr); } #endif // Update pointers in the object body. UpdatingVisitor updating_visitor; obj->IterateBody(type, obj_size, &updating_visitor); return obj_size; } Address MarkCompactCollector::GetForwardingAddressInOldSpace(HeapObject* obj) { // Object should either in old or map space. MapWord encoding = obj->map_word(); // Offset to the first live object's forwarding address. int offset = encoding.DecodeOffset(); Address obj_addr = obj->address(); // Find the first live object's forwarding address. Page* p = Page::FromAddress(obj_addr); Address first_forwarded = p->mc_first_forwarded; // Page start address of forwarded address. Page* forwarded_page = Page::FromAddress(first_forwarded); int forwarded_offset = forwarded_page->Offset(first_forwarded); // Find end of allocation in the page of first_forwarded. int mc_top_offset = forwarded_page->AllocationWatermarkOffset(); // Check if current object's forward pointer is in the same page // as the first live object's forwarding pointer if (forwarded_offset + offset < mc_top_offset) { // In the same page. return first_forwarded + offset; } // Must be in the next page, NOTE: this may cross chunks. Page* next_page = forwarded_page->next_page(); ASSERT(next_page->is_valid()); offset -= (mc_top_offset - forwarded_offset); offset += Page::kObjectStartOffset; ASSERT_PAGE_OFFSET(offset); ASSERT(next_page->OffsetToAddress(offset) < next_page->AllocationTop()); return next_page->OffsetToAddress(offset); } // ------------------------------------------------------------------------- // Phase 4: Relocate objects void MarkCompactCollector::RelocateObjects() { #ifdef DEBUG ASSERT(state_ == UPDATE_POINTERS); state_ = RELOCATE_OBJECTS; #endif // Relocates objects, always relocate map objects first. Relocating // objects in other space relies on map objects to get object size. int live_maps_size = IterateLiveObjects(Heap::map_space(), &RelocateMapObject); int live_pointer_olds_size = IterateLiveObjects(Heap::old_pointer_space(), &RelocateOldPointerObject); int live_data_olds_size = IterateLiveObjects(Heap::old_data_space(), &RelocateOldDataObject); int live_codes_size = IterateLiveObjects(Heap::code_space(), &RelocateCodeObject); int live_cells_size = IterateLiveObjects(Heap::cell_space(), &RelocateCellObject); int live_news_size = IterateLiveObjects(Heap::new_space(), &RelocateNewObject); USE(live_maps_size); USE(live_pointer_olds_size); USE(live_data_olds_size); USE(live_codes_size); USE(live_cells_size); USE(live_news_size); ASSERT(live_maps_size == live_map_objects_size_); ASSERT(live_data_olds_size == live_old_data_objects_size_); ASSERT(live_pointer_olds_size == live_old_pointer_objects_size_); ASSERT(live_codes_size == live_code_objects_size_); ASSERT(live_cells_size == live_cell_objects_size_); ASSERT(live_news_size == live_young_objects_size_); // Flip from and to spaces Heap::new_space()->Flip(); Heap::new_space()->MCCommitRelocationInfo(); // Set age_mark to bottom in to space Address mark = Heap::new_space()->bottom(); Heap::new_space()->set_age_mark(mark); PagedSpaces spaces; for (PagedSpace* space = spaces.next(); space != NULL; space = spaces.next()) space->MCCommitRelocationInfo(); Heap::CheckNewSpaceExpansionCriteria(); Heap::IncrementYoungSurvivorsCounter(live_news_size); } int MarkCompactCollector::RelocateMapObject(HeapObject* obj) { // Recover map pointer. MapWord encoding = obj->map_word(); Address map_addr = encoding.DecodeMapAddress(Heap::map_space()); ASSERT(Heap::map_space()->Contains(HeapObject::FromAddress(map_addr))); // Get forwarding address before resetting map pointer Address new_addr = GetForwardingAddressInOldSpace(obj); // Reset map pointer. The meta map object may not be copied yet so // Map::cast does not yet work. obj->set_map(reinterpret_cast(HeapObject::FromAddress(map_addr))); Address old_addr = obj->address(); if (new_addr != old_addr) { // Move contents. Heap::MoveBlockToOldSpaceAndUpdateRegionMarks(new_addr, old_addr, Map::kSize); } #ifdef DEBUG if (FLAG_gc_verbose) { PrintF("relocate %p -> %p\n", old_addr, new_addr); } #endif return Map::kSize; } static inline int RestoreMap(HeapObject* obj, PagedSpace* space, Address new_addr, Address map_addr) { // This must be a non-map object, and the function relies on the // assumption that the Map space is compacted before the other paged // spaces (see RelocateObjects). // Reset map pointer. obj->set_map(Map::cast(HeapObject::FromAddress(map_addr))); int obj_size = obj->Size(); ASSERT_OBJECT_SIZE(obj_size); ASSERT(space->MCSpaceOffsetForAddress(new_addr) <= space->MCSpaceOffsetForAddress(obj->address())); #ifdef DEBUG if (FLAG_gc_verbose) { PrintF("relocate %p -> %p\n", obj->address(), new_addr); } #endif return obj_size; } int MarkCompactCollector::RelocateOldNonCodeObject(HeapObject* obj, PagedSpace* space) { // Recover map pointer. MapWord encoding = obj->map_word(); Address map_addr = encoding.DecodeMapAddress(Heap::map_space()); ASSERT(Heap::map_space()->Contains(map_addr)); // Get forwarding address before resetting map pointer. Address new_addr = GetForwardingAddressInOldSpace(obj); // Reset the map pointer. int obj_size = RestoreMap(obj, space, new_addr, map_addr); Address old_addr = obj->address(); if (new_addr != old_addr) { // Move contents. if (space == Heap::old_data_space()) { Heap::MoveBlock(new_addr, old_addr, obj_size); } else { Heap::MoveBlockToOldSpaceAndUpdateRegionMarks(new_addr, old_addr, obj_size); } } ASSERT(!HeapObject::FromAddress(new_addr)->IsCode()); HeapObject* copied_to = HeapObject::FromAddress(new_addr); if (copied_to->IsJSFunction()) { PROFILE(FunctionMoveEvent(old_addr, new_addr)); } HEAP_PROFILE(ObjectMoveEvent(old_addr, new_addr)); return obj_size; } int MarkCompactCollector::RelocateOldPointerObject(HeapObject* obj) { return RelocateOldNonCodeObject(obj, Heap::old_pointer_space()); } int MarkCompactCollector::RelocateOldDataObject(HeapObject* obj) { return RelocateOldNonCodeObject(obj, Heap::old_data_space()); } int MarkCompactCollector::RelocateCellObject(HeapObject* obj) { return RelocateOldNonCodeObject(obj, Heap::cell_space()); } int MarkCompactCollector::RelocateCodeObject(HeapObject* obj) { // Recover map pointer. MapWord encoding = obj->map_word(); Address map_addr = encoding.DecodeMapAddress(Heap::map_space()); ASSERT(Heap::map_space()->Contains(HeapObject::FromAddress(map_addr))); // Get forwarding address before resetting map pointer Address new_addr = GetForwardingAddressInOldSpace(obj); // Reset the map pointer. int obj_size = RestoreMap(obj, Heap::code_space(), new_addr, map_addr); Address old_addr = obj->address(); if (new_addr != old_addr) { // Move contents. Heap::MoveBlock(new_addr, old_addr, obj_size); } HeapObject* copied_to = HeapObject::FromAddress(new_addr); if (copied_to->IsCode()) { // May also update inline cache target. Code::cast(copied_to)->Relocate(new_addr - old_addr); // Notify the logger that compiled code has moved. PROFILE(CodeMoveEvent(old_addr, new_addr)); } HEAP_PROFILE(ObjectMoveEvent(old_addr, new_addr)); return obj_size; } int MarkCompactCollector::RelocateNewObject(HeapObject* obj) { int obj_size = obj->Size(); // Get forwarding address Address old_addr = obj->address(); int offset = Heap::new_space()->ToSpaceOffsetForAddress(old_addr); Address new_addr = Memory::Address_at(Heap::new_space()->FromSpaceLow() + offset); #ifdef DEBUG if (Heap::new_space()->FromSpaceContains(new_addr)) { ASSERT(Heap::new_space()->FromSpaceOffsetForAddress(new_addr) <= Heap::new_space()->ToSpaceOffsetForAddress(old_addr)); } else { ASSERT(Heap::TargetSpace(obj) == Heap::old_pointer_space() || Heap::TargetSpace(obj) == Heap::old_data_space()); } #endif // New and old addresses cannot overlap. if (Heap::InNewSpace(HeapObject::FromAddress(new_addr))) { Heap::CopyBlock(new_addr, old_addr, obj_size); } else { Heap::CopyBlockToOldSpaceAndUpdateRegionMarks(new_addr, old_addr, obj_size); } #ifdef DEBUG if (FLAG_gc_verbose) { PrintF("relocate %p -> %p\n", old_addr, new_addr); } #endif HeapObject* copied_to = HeapObject::FromAddress(new_addr); if (copied_to->IsJSFunction()) { PROFILE(FunctionMoveEvent(old_addr, new_addr)); } HEAP_PROFILE(ObjectMoveEvent(old_addr, new_addr)); return obj_size; } void MarkCompactCollector::ReportDeleteIfNeeded(HeapObject* obj) { #ifdef ENABLE_LOGGING_AND_PROFILING if (obj->IsCode()) { PROFILE(CodeDeleteEvent(obj->address())); } else if (obj->IsJSFunction()) { PROFILE(FunctionDeleteEvent(obj->address())); } #endif } } } // namespace v8::internal