diff --git a/deps/v8/include/v8-version.h b/deps/v8/include/v8-version.h
index b2c1e5384eceea..459646b5a4844e 100644
--- a/deps/v8/include/v8-version.h
+++ b/deps/v8/include/v8-version.h
@@ -11,7 +11,7 @@
 #define V8_MAJOR_VERSION 6
 #define V8_MINOR_VERSION 1
 #define V8_BUILD_NUMBER 534
-#define V8_PATCH_LEVEL 42
+#define V8_PATCH_LEVEL 45
 
 // Use 1 for candidates and 0 otherwise.
 // (Boolean macro values are not supported by all preprocessors.)
diff --git a/deps/v8/src/heap/gc-tracer.cc b/deps/v8/src/heap/gc-tracer.cc
index d675492a3abc1c..a28bc65f75de73 100644
--- a/deps/v8/src/heap/gc-tracer.cc
+++ b/deps/v8/src/heap/gc-tracer.cc
@@ -490,6 +490,8 @@ void GCTracer::PrintNVP() const {
           "promotion_rate=%.1f%% "
           "semi_space_copy_rate=%.1f%% "
           "new_space_allocation_throughput=%.1f "
+          "unmapper_chunks=%d "
+          "unmapper_delayed_chunks=%d "
           "context_disposal_rate=%.1f\n",
           duration, spent_in_mutator, current_.TypeName(true),
           current_.reduce_memory, current_.scopes[Scope::HEAP_PROLOGUE],
@@ -517,6 +519,8 @@ void GCTracer::PrintNVP() const {
           AverageSurvivalRatio(), heap_->promotion_rate_,
           heap_->semi_space_copied_rate_,
           NewSpaceAllocationThroughputInBytesPerMillisecond(),
+          heap_->memory_allocator()->unmapper()->NumberOfChunks(),
+          heap_->memory_allocator()->unmapper()->NumberOfDelayedChunks(),
           ContextDisposalRateInMilliseconds());
       break;
     case Event::MINOR_MARK_COMPACTOR:
@@ -650,6 +654,8 @@ void GCTracer::PrintNVP() const {
           "promotion_rate=%.1f%% "
           "semi_space_copy_rate=%.1f%% "
           "new_space_allocation_throughput=%.1f "
+          "unmapper_chunks=%d "
+          "unmapper_delayed_chunks=%d "
           "context_disposal_rate=%.1f "
           "compaction_speed=%.f\n",
           duration, spent_in_mutator, current_.TypeName(true),
@@ -726,6 +732,8 @@ void GCTracer::PrintNVP() const {
           AverageSurvivalRatio(), heap_->promotion_rate_,
           heap_->semi_space_copied_rate_,
           NewSpaceAllocationThroughputInBytesPerMillisecond(),
+          heap_->memory_allocator()->unmapper()->NumberOfChunks(),
+          heap_->memory_allocator()->unmapper()->NumberOfDelayedChunks(),
           ContextDisposalRateInMilliseconds(),
           CompactionSpeedInBytesPerMillisecond());
       break;
diff --git a/deps/v8/src/heap/heap.cc b/deps/v8/src/heap/heap.cc
index 65526f748c4e6d..62a5856f346137 100644
--- a/deps/v8/src/heap/heap.cc
+++ b/deps/v8/src/heap/heap.cc
@@ -1716,6 +1716,12 @@ void Heap::Scavenge() {
   IncrementalMarking::PauseBlackAllocationScope pause_black_allocation(
       incremental_marking());
 
+  if (mark_compact_collector()->sweeper().sweeping_in_progress() &&
+      memory_allocator_->unmapper()->NumberOfDelayedChunks() >
+          static_cast<int>(new_space_->MaximumCapacity() / Page::kPageSize)) {
+    mark_compact_collector()->EnsureSweepingCompleted();
+  }
+
   mark_compact_collector()->sweeper().EnsureNewSpaceCompleted();
 
   SetGCState(SCAVENGE);
diff --git a/deps/v8/src/heap/spaces.cc b/deps/v8/src/heap/spaces.cc
index 798ef89ec1f201..39a362d6a0504d 100644
--- a/deps/v8/src/heap/spaces.cc
+++ b/deps/v8/src/heap/spaces.cc
@@ -418,6 +418,15 @@ void MemoryAllocator::Unmapper::ReconsiderDelayedChunks() {
   }
 }
 
+int MemoryAllocator::Unmapper::NumberOfChunks() {
+  base::LockGuard<base::Mutex> guard(&mutex_);
+  size_t result = 0;
+  for (int i = 0; i < kNumberOfChunkQueues; i++) {
+    result += chunks_[i].size();
+  }
+  return static_cast<int>(result);
+}
+
 bool MemoryAllocator::CanFreeMemoryChunk(MemoryChunk* chunk) {
   MarkCompactCollector* mc = isolate_->heap()->mark_compact_collector();
   // We cannot free a memory chunk in new space while the sweeper is running
diff --git a/deps/v8/src/heap/spaces.h b/deps/v8/src/heap/spaces.h
index 2ae089b4011f70..045469aa56d820 100644
--- a/deps/v8/src/heap/spaces.h
+++ b/deps/v8/src/heap/spaces.h
@@ -1226,6 +1226,13 @@ class V8_EXPORT_PRIVATE MemoryAllocator {
 
     bool has_delayed_chunks() { return delayed_regular_chunks_.size() > 0; }
 
+    int NumberOfDelayedChunks() {
+      base::LockGuard<base::Mutex> guard(&mutex_);
+      return static_cast<int>(delayed_regular_chunks_.size());
+    }
+
+    int NumberOfChunks();
+
    private:
     static const int kReservedQueueingSlots = 64;
     static const int kMaxUnmapperTasks = 24;