Tweak compaction candidate selection to avoid keeping page with low occupancy around.

src/heap.cc

 // Copyright 2012 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 218 matching lines @@
 
 
 int Heap::GcSafeSizeOfOldObject(HeapObject* object) {
   if (IntrusiveMarking::IsMarked(object)) {
     return IntrusiveMarking::SizeOfMarkedObject(object);
   }
   return object->SizeFromMap(object->map());
 }
 
 
-GarbageCollector Heap::SelectGarbageCollector(AllocationSpace space) {
+GarbageCollector Heap::SelectGarbageCollector(AllocationSpace space,
+                                              const char** reason) {
   // Is global GC requested?
   if (space != NEW_SPACE || FLAG_gc_global) {
     isolate_->counters()->gc_compactor_caused_by_request()->Increment();
+    *reason = "GC in old space requested";
     return MARK_COMPACTOR;
   }
 
   // Is enough data promoted to justify a global GC?
   if (OldGenerationPromotionLimitReached()) {
     isolate_->counters()->gc_compactor_caused_by_promoted_data()->Increment();
+    *reason = "promotion limit reached";
     return MARK_COMPACTOR;
   }
 
   // Have allocation in OLD and LO failed?
   if (old_gen_exhausted_) {
     isolate_->counters()->
         gc_compactor_caused_by_oldspace_exhaustion()->Increment();
+    *reason = "old generations exhausted";
     return MARK_COMPACTOR;
   }
 
   // Is there enough space left in OLD to guarantee that a scavenge can
   // succeed?
   //
   // Note that MemoryAllocator->MaxAvailable() undercounts the memory available
   // for object promotion. It counts only the bytes that the memory
   // allocator has not yet allocated from the OS and assigned to any space,
   // and does not count available bytes already in the old space or code
   // space.  Undercounting is safe---we may get an unrequested full GC when
   // a scavenge would have succeeded.
   if (isolate_->memory_allocator()->MaxAvailable() <= new_space_.Size()) {
     isolate_->counters()->
         gc_compactor_caused_by_oldspace_exhaustion()->Increment();
+    *reason = "scavenge might not succeed";
     return MARK_COMPACTOR;
   }
 
   // Default
+  *reason = NULL;
   return SCAVENGER;
 }
 
 
 // TODO(1238405): Combine the infrastructure for --heap-stats and
 // --log-gc to avoid the complicated preprocessor and flag testing.
 void Heap::ReportStatisticsBeforeGC() {
   // Heap::ReportHeapStatistics will also log NewSpace statistics when
   // compiled --log-gc is set.  The following logic is used to avoid
   // double logging.
@@ skipping 139 matching lines @@
       symbol_table()->NumberOfElements());
 #if defined(DEBUG)
   ReportStatisticsAfterGC();
 #endif  // DEBUG
 #ifdef ENABLE_DEBUGGER_SUPPORT
   isolate_->debug()->AfterGarbageCollection();
 #endif  // ENABLE_DEBUGGER_SUPPORT
 }
 
 
-void Heap::CollectAllGarbage(int flags) {
+void Heap::CollectAllGarbage(int flags, const char* gc_reason) {
   // Since we are ignoring the return value, the exact choice of space does
   // not matter, so long as we do not specify NEW_SPACE, which would not
   // cause a full GC.
   mark_compact_collector_.SetFlags(flags);
-  CollectGarbage(OLD_POINTER_SPACE);
+  CollectGarbage(OLD_POINTER_SPACE, gc_reason);
   mark_compact_collector_.SetFlags(kNoGCFlags);
 }
 
 
-void Heap::CollectAllAvailableGarbage() {
+void Heap::CollectAllAvailableGarbage(const char* gc_reason) {
   // Since we are ignoring the return value, the exact choice of space does
   // not matter, so long as we do not specify NEW_SPACE, which would not
   // cause a full GC.
   // Major GC would invoke weak handle callbacks on weakly reachable
   // handles, but won't collect weakly reachable objects until next
   // major GC.  Therefore if we collect aggressively and weak handle callback
   // has been invoked, we rerun major GC to release objects which become
   // garbage.
   // Note: as weak callbacks can execute arbitrary code, we cannot
   // hope that eventually there will be no weak callbacks invocations.
   // Therefore stop recollecting after several attempts.
-  mark_compact_collector()->SetFlags(kMakeHeapIterableMask);
+  mark_compact_collector()->SetFlags(kMakeHeapIterableMask |
+                                     kReduceMemoryFootprintMask);
   isolate_->compilation_cache()->Clear();
   const int kMaxNumberOfAttempts = 7;
   for (int attempt = 0; attempt < kMaxNumberOfAttempts; attempt++) {
-    if (!CollectGarbage(OLD_POINTER_SPACE, MARK_COMPACTOR)) {
+    if (!CollectGarbage(OLD_POINTER_SPACE, MARK_COMPACTOR, gc_reason, NULL)) {
       break;
     }
   }
   mark_compact_collector()->SetFlags(kNoGCFlags);
   new_space_.Shrink();
   UncommitFromSpace();
   Shrink();
   incremental_marking()->UncommitMarkingDeque();
 }
 
 
-bool Heap::CollectGarbage(AllocationSpace space, GarbageCollector collector) {
+bool Heap::CollectGarbage(AllocationSpace space,
+                          GarbageCollector collector,
+                          const char* gc_reason,
+                          const char* collector_reason) {
   // The VM is in the GC state until exiting this function.
   VMState state(isolate_, GC);
 
 #ifdef DEBUG
   // Reset the allocation timeout to the GC interval, but make sure to
   // allow at least a few allocations after a collection. The reason
   // for this is that we have a lot of allocation sequences and we
   // assume that a garbage collection will allow the subsequent
   // allocation attempts to go through.
   allocation_timeout_ = Max(6, FLAG_gc_interval);
 #endif
 
   if (collector == SCAVENGER && !incremental_marking()->IsStopped()) {
     if (FLAG_trace_incremental_marking) {
       PrintF("[IncrementalMarking] Scavenge during marking.\n");
     }
   }
 
   if (collector == MARK_COMPACTOR &&
       !mark_compact_collector()->PreciseSweepingRequired() &&
       !incremental_marking()->IsStopped() &&
       !incremental_marking()->should_hurry() &&
       FLAG_incremental_marking_steps) {
     if (FLAG_trace_incremental_marking) {
       PrintF("[IncrementalMarking] Delaying MarkSweep.\n");
     }
     collector = SCAVENGER;
+    collector_reason = "incremental marking delaying mark-sweep";
   }
 
   bool next_gc_likely_to_collect_more = false;
 
-  { GCTracer tracer(this);
+  { GCTracer tracer(this, gc_reason, collector_reason);
     GarbageCollectionPrologue();
     // The GC count was incremented in the prologue.  Tell the tracer about
     // it.
     tracer.set_gc_count(gc_count_);
 
     // Tell the tracer which collector we've selected.
     tracer.set_collector(collector);
 
     HistogramTimer* rate = (collector == SCAVENGER)
         ? isolate_->counters()->gc_scavenger()
@@ skipping 11 matching lines @@
     if (incremental_marking()->WorthActivating() && NextGCIsLikelyToBeFull()) {
       incremental_marking()->Start();
     }
   }
 
   return next_gc_likely_to_collect_more;
 }
 
 
 void Heap::PerformScavenge() {
-  GCTracer tracer(this);
+  GCTracer tracer(this, NULL, NULL);
   if (incremental_marking()->IsStopped()) {
     PerformGarbageCollection(SCAVENGER, &tracer);
   } else {
     PerformGarbageCollection(MARK_COMPACTOR, &tracer);
   }
 }
 
 
 #ifdef DEBUG
 // Helper class for verifying the symbol table.
@@ skipping 34 matching lines @@
   PagedSpace* code_space = Heap::code_space();
   PagedSpace* map_space = Heap::map_space();
   PagedSpace* cell_space = Heap::cell_space();
   LargeObjectSpace* lo_space = Heap::lo_space();
   bool gc_performed = true;
   int counter = 0;
   static const int kThreshold = 20;
   while (gc_performed && counter++ < kThreshold) {
     gc_performed = false;
     if (!new_space->ReserveSpace(new_space_size)) {
-      Heap::CollectGarbage(NEW_SPACE);
+      Heap::CollectGarbage(NEW_SPACE,
+                           "failed to reserve space in the new space");
       gc_performed = true;
     }
     if (!old_pointer_space->ReserveSpace(pointer_space_size)) {
-      Heap::CollectGarbage(OLD_POINTER_SPACE);
+      Heap::CollectGarbage(OLD_POINTER_SPACE,
+                           "failed to reserve space in the old pointer space");
       gc_performed = true;
     }
     if (!(old_data_space->ReserveSpace(data_space_size))) {
-      Heap::CollectGarbage(OLD_DATA_SPACE);
+      Heap::CollectGarbage(OLD_DATA_SPACE,
+                           "failed to reserve space in the old data space");
       gc_performed = true;
     }
     if (!(code_space->ReserveSpace(code_space_size))) {
-      Heap::CollectGarbage(CODE_SPACE);
+      Heap::CollectGarbage(CODE_SPACE,
+                           "failed to reserve space in the code space");
       gc_performed = true;
     }
     if (!(map_space->ReserveSpace(map_space_size))) {
-      Heap::CollectGarbage(MAP_SPACE);
+      Heap::CollectGarbage(MAP_SPACE,
+                           "failed to reserve space in the map space");
       gc_performed = true;
     }
     if (!(cell_space->ReserveSpace(cell_space_size))) {
-      Heap::CollectGarbage(CELL_SPACE);
+      Heap::CollectGarbage(CELL_SPACE,
+                           "failed to reserve space in the cell space");
       gc_performed = true;
     }
     // We add a slack-factor of 2 in order to have space for a series of
     // large-object allocations that are only just larger than the page size.
     large_object_size *= 2;
     // The ReserveSpace method on the large object space checks how much
     // we can expand the old generation.  This includes expansion caused by
     // allocation in the other spaces.
     large_object_size += cell_space_size + map_space_size + code_space_size +
         data_space_size + pointer_space_size;
     if (!(lo_space->ReserveSpace(large_object_size))) {
-      Heap::CollectGarbage(LO_SPACE);
+      Heap::CollectGarbage(LO_SPACE,
+                           "failed to reserve space in the large object space");
       gc_performed = true;
     }
   }
 
   if (gc_performed) {
     // Failed to reserve the space after several attempts.
     V8::FatalProcessOutOfMemory("Heap::ReserveSpace");
   }
 }
 
@@ skipping 4101 matching lines @@
 
 bool Heap::IsHeapIterable() {
   return (!old_pointer_space()->was_swept_conservatively() &&
           !old_data_space()->was_swept_conservatively());
 }
 
 
 void Heap::EnsureHeapIsIterable() {
   ASSERT(IsAllocationAllowed());
   if (!IsHeapIterable()) {
-    CollectAllGarbage(kMakeHeapIterableMask);
+    CollectAllGarbage(kMakeHeapIterableMask, "Heap::EnsureHeapIsIterable");
   }
   ASSERT(IsHeapIterable());
 }
 
 
 bool Heap::IdleNotification(int hint) {
   if (hint >= 1000) return IdleGlobalGC();
   if (contexts_disposed_ > 0 || !FLAG_incremental_marking ||
       FLAG_expose_gc || Serializer::enabled()) {
     return true;
@@ skipping 49 matching lines @@
   incremental_marking()->Step(step_size);
   idle_notification_will_schedule_next_gc_ = false;
 
   if (incremental_marking()->IsComplete()) {
     bool uncommit = false;
     if (gc_count_at_last_idle_gc_ == gc_count_) {
       // No GC since the last full GC, the mutator is probably not active.
       isolate_->compilation_cache()->Clear();
       uncommit = true;
     }
-    CollectAllGarbage(kNoGCFlags);
+    CollectAllGarbage(kNoGCFlags, "idle notification: finalize incremental");
     gc_count_at_last_idle_gc_ = gc_count_;
     if (uncommit) {
       new_space_.Shrink();
       UncommitFromSpace();
     }
   }
   return false;
 }
 
 
@@ skipping 20 matching lines @@
     number_idle_notifications_ =
         Min(number_idle_notifications_ + 1, kMaxIdleCount);
   } else {
     number_idle_notifications_ = 0;
     last_idle_notification_gc_count_ = gc_count_;
   }
 
   if (number_idle_notifications_ == kIdlesBeforeScavenge) {
     if (contexts_disposed_ > 0) {
       HistogramTimerScope scope(isolate_->counters()->gc_context());
-      CollectAllGarbage(kNoGCFlags);
+      CollectAllGarbage(kReduceMemoryFootprintMask,
+                        "idle notification: contexts disposed");
     } else {
-      CollectGarbage(NEW_SPACE);
+      CollectGarbage(NEW_SPACE, "idle notification");
     }
     new_space_.Shrink();
     last_idle_notification_gc_count_ = gc_count_;
   } else if (number_idle_notifications_ == kIdlesBeforeMarkSweep) {
     // Before doing the mark-sweep collections we clear the
     // compilation cache to avoid hanging on to source code and
     // generated code for cached functions.
     isolate_->compilation_cache()->Clear();
 
-    CollectAllGarbage(kNoGCFlags);
+    CollectAllGarbage(kReduceMemoryFootprintMask, "idle notification");
     new_space_.Shrink();
     last_idle_notification_gc_count_ = gc_count_;
 
   } else if (number_idle_notifications_ == kIdlesBeforeMarkCompact) {
-    CollectAllGarbage(kNoGCFlags);
+    CollectAllGarbage(kReduceMemoryFootprintMask, "idle notification");
     new_space_.Shrink();
     last_idle_notification_gc_count_ = gc_count_;
     number_idle_notifications_ = 0;
     finished = true;
   } else if (contexts_disposed_ > 0) {
     if (FLAG_expose_gc) {
       contexts_disposed_ = 0;
     } else {
       HistogramTimerScope scope(isolate_->counters()->gc_context());
-      CollectAllGarbage(kNoGCFlags);
+      CollectAllGarbage(kReduceMemoryFootprintMask,
+                        "idle notification: contexts disposed");
       last_idle_notification_gc_count_ = gc_count_;
     }
     // If this is the first idle notification, we reset the
     // notification count to avoid letting idle notifications for
     // context disposal garbage collections start a potentially too
     // aggressive idle GC cycle.
     if (number_idle_notifications_ <= 1) {
       number_idle_notifications_ = 0;
       uncommit = false;
     }
@@ skipping 1610 matching lines @@
   OldSpaces spaces;
   for (OldSpace* space = spaces.next();
        space != NULL;
        space = spaces.next()) {
     holes_size += space->Waste() + space->Available();
   }
   return holes_size;
 }
 
 
-GCTracer::GCTracer(Heap* heap)
+GCTracer::GCTracer(Heap* heap,
+                   const char* gc_reason,
+                   const char* collector_reason)
     : start_time_(0.0),
-      start_size_(0),
+      start_object_size_(0),
+      start_memory_size_(0),
       gc_count_(0),
       full_gc_count_(0),
       allocated_since_last_gc_(0),
       spent_in_mutator_(0),
       promoted_objects_size_(0),
-      heap_(heap) {
+      heap_(heap),
+      gc_reason_(gc_reason),
+      collector_reason_(collector_reason) {
   if (!FLAG_trace_gc && !FLAG_print_cumulative_gc_stat) return;
   start_time_ = OS::TimeCurrentMillis();
-  start_size_ = heap_->SizeOfObjects();
+  start_object_size_ = heap_->SizeOfObjects();
+  start_memory_size_ = heap_->isolate()->memory_allocator()->Size();
 
   for (int i = 0; i < Scope::kNumberOfScopes; i++) {
     scopes_[i] = 0;
   }
 
   in_free_list_or_wasted_before_gc_ = CountTotalHolesSize();
 
   allocated_since_last_gc_ =
       heap_->SizeOfObjects() - heap_->alive_after_last_gc_;
 
@@ skipping 29 matching lines @@
                                      heap_->alive_after_last_gc_);
     if (!first_gc) {
       heap_->min_in_mutator_ = Min(heap_->min_in_mutator_,
                                    static_cast<int>(spent_in_mutator_));
     }
   }
 
   if (!FLAG_trace_gc_nvp) {
     int external_time = static_cast<int>(scopes_[Scope::EXTERNAL]);
 
-    PrintF("%s %.1f -> %.1f MB, ",
+    double end_memory_size_mb =
+        static_cast<double>(heap_->isolate()->memory_allocator()->Size()) / MB;
+
+    PrintF("%s %.1f (%.1f) -> %.1f (%.1f) MB, ",
            CollectorString(),
-           static_cast<double>(start_size_) / MB,
-           SizeOfHeapObjects());
+           static_cast<double>(start_object_size_) / MB,
+           static_cast<double>(start_memory_size_) / MB,
+           SizeOfHeapObjects(),
+           end_memory_size_mb);
 
     if (external_time > 0) PrintF("%d / ", external_time);
     PrintF("%d ms", time);
     if (steps_count_ > 0) {
       if (collector_ == SCAVENGER) {
         PrintF(" (+ %d ms in %d steps since last GC)",
                static_cast<int>(steps_took_since_last_gc_),
                steps_count_since_last_gc_);
       } else {
         PrintF(" (+ %d ms in %d steps since start of marking, "
                    "biggest step %f ms)",
                static_cast<int>(steps_took_),
                steps_count_,
                longest_step_);
       }
     }
+
+    if (gc_reason_ != NULL) {
+      PrintF(" [%s]", gc_reason_);
+    }
+
+    if (collector_reason_ != NULL) {
+      PrintF(" [%s]", collector_reason_);
+    }
+
     PrintF(".\n");
   } else {
     PrintF("pause=%d ", time);
     PrintF("mutator=%d ",
            static_cast<int>(spent_in_mutator_));
 
     PrintF("gc=");
     switch (collector_) {
       case SCAVENGER:
         PrintF("s");
@@ skipping 17 matching lines @@
            static_cast<int>(scopes_[Scope::MC_UPDATE_ROOT_TO_NEW_POINTERS]));
     PrintF("old_new=%d ",
            static_cast<int>(scopes_[Scope::MC_UPDATE_OLD_TO_NEW_POINTERS]));
     PrintF("compaction_ptrs=%d ",
            static_cast<int>(scopes_[Scope::MC_UPDATE_POINTERS_TO_EVACUATED]));
     PrintF("intracompaction_ptrs=%d ", static_cast<int>(scopes_[
         Scope::MC_UPDATE_POINTERS_BETWEEN_EVACUATED]));
     PrintF("misc_compaction=%d ",
            static_cast<int>(scopes_[Scope::MC_UPDATE_MISC_POINTERS]));
 
-    PrintF("total_size_before=%" V8_PTR_PREFIX "d ", start_size_);
+    PrintF("total_size_before=%" V8_PTR_PREFIX "d ", start_object_size_);
     PrintF("total_size_after=%" V8_PTR_PREFIX "d ", heap_->SizeOfObjects());
     PrintF("holes_size_before=%" V8_PTR_PREFIX "d ",
            in_free_list_or_wasted_before_gc_);
     PrintF("holes_size_after=%" V8_PTR_PREFIX "d ", CountTotalHolesSize());
 
     PrintF("allocated=%" V8_PTR_PREFIX "d ", allocated_since_last_gc_);
     PrintF("promoted=%" V8_PTR_PREFIX "d ", promoted_objects_size_);
 
     if (collector_ == SCAVENGER) {
       PrintF("stepscount=%d ", steps_count_since_last_gc_);
@@ skipping 195 matching lines @@
   isolate_->heap()->store_buffer()->Compact();
   isolate_->heap()->store_buffer()->Filter(MemoryChunk::ABOUT_TO_BE_FREED);
   for (chunk = chunks_queued_for_free_; chunk != NULL; chunk = next) {
     next = chunk->next_chunk();
     isolate_->memory_allocator()->Free(chunk);
   }
   chunks_queued_for_free_ = NULL;
 }
 
 } }  // namespace v8::internal