[heap] Only reclaim inaccessible memory when reducing memory.

Bug: chromium:897074
Change-Id: I65894046064a230847f3e629e56d8a171546aa51
Reviewed-on: https://chromium-review.googlesource.com/c/1293950Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Hannes Payer <hpayer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56877}

src/heap/sweeper.cc

@@ -15,6 +15,20 @@
 namespace v8 {
 namespace internal {
 
+Sweeper::Sweeper(Heap* heap, MajorNonAtomicMarkingState* marking_state)
+    : heap_(heap),
+      marking_state_(marking_state),
+      num_tasks_(0),
+      pending_sweeper_tasks_semaphore_(0),
+      incremental_sweeper_pending_(false),
+      sweeping_in_progress_(false),
+      num_sweeping_tasks_(0),
+      stop_sweeper_tasks_(false),
+      iterability_task_semaphore_(0),
+      iterability_in_progress_(false),
+      iterability_task_started_(false),
+      should_reduce_memory_(heap->ShouldReduceMemory()) {}
+
 Sweeper::PauseOrCompleteScope::PauseOrCompleteScope(Sweeper* sweeper)
     : sweeper_(sweeper) {
   sweeper_->stop_sweeper_tasks_ = true;
@@ -289,7 +303,7 @@ int Sweeper::RawSweep(Page* p, FreeListRebuildingMode free_list_mode,
             free_start, static_cast<int>(size), ClearRecordedSlots::kNo,
             ClearFreedMemoryMode::kClearFreedMemory);
       }
-      p->DiscardUnusedMemory(free_start, size);
+      if (should_reduce_memory_) p->DiscardUnusedMemory(free_start, size);
       RememberedSet<OLD_TO_NEW>::RemoveRange(p, free_start, free_end,
                                              SlotSet::KEEP_EMPTY_BUCKETS);
       RememberedSet<OLD_TO_OLD>::RemoveRange(p, free_start, free_end,
@@ -330,7 +344,7 @@ int Sweeper::RawSweep(Page* p, FreeListRebuildingMode free_list_mode,
                                       ClearRecordedSlots::kNo,
                                       ClearFreedMemoryMode::kClearFreedMemory);
     }
-    p->DiscardUnusedMemory(free_start, size);
+    if (should_reduce_memory_) p->DiscardUnusedMemory(free_start, size);
     RememberedSet<OLD_TO_NEW>::RemoveRange(p, free_start, p->area_end(),
                                            SlotSet::KEEP_EMPTY_BUCKETS);
     RememberedSet<OLD_TO_OLD>::RemoveRange(p, free_start, p->area_end(),

src/heap/sweeper.h

@@ -77,18 +77,7 @@ class Sweeper {
   };
   enum AddPageMode { REGULAR, READD_TEMPORARY_REMOVED_PAGE };
 
-  Sweeper(Heap* heap, MajorNonAtomicMarkingState* marking_state)
-      : heap_(heap),
-        marking_state_(marking_state),
-        num_tasks_(0),
-        pending_sweeper_tasks_semaphore_(0),
-        incremental_sweeper_pending_(false),
-        sweeping_in_progress_(false),
-        num_sweeping_tasks_(0),
-        stop_sweeper_tasks_(false),
-        iterability_task_semaphore_(0),
-        iterability_in_progress_(false),
-        iterability_task_started_(false) {}
+  Sweeper(Heap* heap, MajorNonAtomicMarkingState* marking_state);
 
   bool sweeping_in_progress() const { return sweeping_in_progress_; }
 
@@ -196,6 +185,7 @@ class Sweeper {
   base::Semaphore iterability_task_semaphore_;
   bool iterability_in_progress_;
   bool iterability_task_started_;
+  bool should_reduce_memory_;
 };
 
 }  // namespace internal