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      1 // Copyright 2015 the V8 project authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 #include "src/heap/memory-reducer.h"
      6 
      7 #include "src/flags.h"
      8 #include "src/heap/gc-tracer.h"
      9 #include "src/heap/heap-inl.h"
     10 #include "src/utils.h"
     11 #include "src/v8.h"
     12 
     13 namespace v8 {
     14 namespace internal {
     15 
     16 const int MemoryReducer::kLongDelayMs = 8000;
     17 const int MemoryReducer::kShortDelayMs = 500;
     18 const int MemoryReducer::kWatchdogDelayMs = 100000;
     19 const int MemoryReducer::kMaxNumberOfGCs = 3;
     20 
     21 MemoryReducer::TimerTask::TimerTask(MemoryReducer* memory_reducer)
     22     : CancelableTask(memory_reducer->heap()->isolate()),
     23       memory_reducer_(memory_reducer) {}
     24 
     25 
     26 void MemoryReducer::TimerTask::RunInternal() {
     27   Heap* heap = memory_reducer_->heap();
     28   Event event;
     29   double time_ms = heap->MonotonicallyIncreasingTimeInMs();
     30   heap->tracer()->SampleAllocation(time_ms, heap->NewSpaceAllocationCounter(),
     31                                    heap->OldGenerationAllocationCounter());
     32   bool low_allocation_rate = heap->HasLowAllocationRate();
     33   bool optimize_for_memory = heap->ShouldOptimizeForMemoryUsage();
     34   if (FLAG_trace_gc_verbose) {
     35     heap->isolate()->PrintWithTimestamp(
     36         "Memory reducer: %s, %s\n",
     37         low_allocation_rate ? "low alloc" : "high alloc",
     38         optimize_for_memory ? "background" : "foreground");
     39   }
     40   event.type = kTimer;
     41   event.time_ms = time_ms;
     42   // The memory reducer will start incremental markig if
     43   // 1) mutator is likely idle: js call rate is low and allocation rate is low.
     44   // 2) mutator is in background: optimize for memory flag is set.
     45   event.should_start_incremental_gc =
     46       low_allocation_rate || optimize_for_memory;
     47   event.can_start_incremental_gc =
     48       heap->incremental_marking()->IsStopped() &&
     49       (heap->incremental_marking()->CanBeActivated() || optimize_for_memory);
     50   memory_reducer_->NotifyTimer(event);
     51 }
     52 
     53 
     54 void MemoryReducer::NotifyTimer(const Event& event) {
     55   DCHECK_EQ(kTimer, event.type);
     56   DCHECK_EQ(kWait, state_.action);
     57   state_ = Step(state_, event);
     58   if (state_.action == kRun) {
     59     DCHECK(heap()->incremental_marking()->IsStopped());
     60     DCHECK(FLAG_incremental_marking);
     61     if (FLAG_trace_gc_verbose) {
     62       heap()->isolate()->PrintWithTimestamp("Memory reducer: started GC #%d\n",
     63                                             state_.started_gcs);
     64     }
     65     heap()->StartIdleIncrementalMarking(
     66         GarbageCollectionReason::kMemoryReducer);
     67   } else if (state_.action == kWait) {
     68     if (!heap()->incremental_marking()->IsStopped() &&
     69         heap()->ShouldOptimizeForMemoryUsage()) {
     70       // Make progress with pending incremental marking if memory usage has
     71       // higher priority than latency. This is important for background tabs
     72       // that do not send idle notifications.
     73       const int kIncrementalMarkingDelayMs = 500;
     74       double deadline = heap()->MonotonicallyIncreasingTimeInMs() +
     75                         kIncrementalMarkingDelayMs;
     76       heap()->incremental_marking()->AdvanceIncrementalMarking(
     77           deadline, IncrementalMarking::NO_GC_VIA_STACK_GUARD,
     78           IncrementalMarking::FORCE_COMPLETION, StepOrigin::kTask);
     79       heap()->FinalizeIncrementalMarkingIfComplete(
     80           GarbageCollectionReason::kFinalizeMarkingViaTask);
     81     }
     82     // Re-schedule the timer.
     83     ScheduleTimer(event.time_ms, state_.next_gc_start_ms - event.time_ms);
     84     if (FLAG_trace_gc_verbose) {
     85       heap()->isolate()->PrintWithTimestamp(
     86           "Memory reducer: waiting for %.f ms\n",
     87           state_.next_gc_start_ms - event.time_ms);
     88     }
     89   }
     90 }
     91 
     92 
     93 void MemoryReducer::NotifyMarkCompact(const Event& event) {
     94   DCHECK_EQ(kMarkCompact, event.type);
     95   Action old_action = state_.action;
     96   state_ = Step(state_, event);
     97   if (old_action != kWait && state_.action == kWait) {
     98     // If we are transitioning to the WAIT state, start the timer.
     99     ScheduleTimer(event.time_ms, state_.next_gc_start_ms - event.time_ms);
    100   }
    101   if (old_action == kRun) {
    102     if (FLAG_trace_gc_verbose) {
    103       heap()->isolate()->PrintWithTimestamp(
    104           "Memory reducer: finished GC #%d (%s)\n", state_.started_gcs,
    105           state_.action == kWait ? "will do more" : "done");
    106     }
    107   }
    108 }
    109 
    110 void MemoryReducer::NotifyPossibleGarbage(const Event& event) {
    111   DCHECK_EQ(kPossibleGarbage, event.type);
    112   Action old_action = state_.action;
    113   state_ = Step(state_, event);
    114   if (old_action != kWait && state_.action == kWait) {
    115     // If we are transitioning to the WAIT state, start the timer.
    116     ScheduleTimer(event.time_ms, state_.next_gc_start_ms - event.time_ms);
    117   }
    118 }
    119 
    120 
    121 bool MemoryReducer::WatchdogGC(const State& state, const Event& event) {
    122   return state.last_gc_time_ms != 0 &&
    123          event.time_ms > state.last_gc_time_ms + kWatchdogDelayMs;
    124 }
    125 
    126 
    127 // For specification of this function see the comment for MemoryReducer class.
    128 MemoryReducer::State MemoryReducer::Step(const State& state,
    129                                          const Event& event) {
    130   if (!FLAG_incremental_marking || !FLAG_memory_reducer) {
    131     return State(kDone, 0, 0, state.last_gc_time_ms);
    132   }
    133   switch (state.action) {
    134     case kDone:
    135       if (event.type == kTimer) {
    136         return state;
    137       } else {
    138         DCHECK(event.type == kPossibleGarbage || event.type == kMarkCompact);
    139         return State(
    140             kWait, 0, event.time_ms + kLongDelayMs,
    141             event.type == kMarkCompact ? event.time_ms : state.last_gc_time_ms);
    142       }
    143     case kWait:
    144       switch (event.type) {
    145         case kPossibleGarbage:
    146           return state;
    147         case kTimer:
    148           if (state.started_gcs >= kMaxNumberOfGCs) {
    149             return State(kDone, kMaxNumberOfGCs, 0.0, state.last_gc_time_ms);
    150           } else if (event.can_start_incremental_gc &&
    151                      (event.should_start_incremental_gc ||
    152                       WatchdogGC(state, event))) {
    153             if (state.next_gc_start_ms <= event.time_ms) {
    154               return State(kRun, state.started_gcs + 1, 0.0,
    155                            state.last_gc_time_ms);
    156             } else {
    157               return state;
    158             }
    159           } else {
    160             return State(kWait, state.started_gcs, event.time_ms + kLongDelayMs,
    161                          state.last_gc_time_ms);
    162           }
    163         case kMarkCompact:
    164           return State(kWait, state.started_gcs, event.time_ms + kLongDelayMs,
    165                        event.time_ms);
    166       }
    167     case kRun:
    168       if (event.type != kMarkCompact) {
    169         return state;
    170       } else {
    171         if (state.started_gcs < kMaxNumberOfGCs &&
    172             (event.next_gc_likely_to_collect_more || state.started_gcs == 1)) {
    173           return State(kWait, state.started_gcs, event.time_ms + kShortDelayMs,
    174                        event.time_ms);
    175         } else {
    176           return State(kDone, kMaxNumberOfGCs, 0.0, event.time_ms);
    177         }
    178       }
    179   }
    180   UNREACHABLE();
    181   return State(kDone, 0, 0, 0.0);  // Make the compiler happy.
    182 }
    183 
    184 
    185 void MemoryReducer::ScheduleTimer(double time_ms, double delay_ms) {
    186   DCHECK(delay_ms > 0);
    187   // Leave some room for precision error in task scheduler.
    188   const double kSlackMs = 100;
    189   v8::Isolate* isolate = reinterpret_cast<v8::Isolate*>(heap()->isolate());
    190   auto timer_task = new MemoryReducer::TimerTask(this);
    191   V8::GetCurrentPlatform()->CallDelayedOnForegroundThread(
    192       isolate, timer_task, (delay_ms + kSlackMs) / 1000.0);
    193 }
    194 
    195 void MemoryReducer::TearDown() { state_ = State(kDone, 0, 0, 0.0); }
    196 
    197 }  // namespace internal
    198 }  // namespace v8
    199