Activate memory reducer for small heaps in background tabs.

src/heap/heap.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/heap/heap.h"
 
 #include "src/accessors.h"
 #include "src/api.h"
 #include "src/ast/scopeinfo.h"
 #include "src/base/bits.h"
@@ skipping 1042 matching lines @@
 
   return next_gc_likely_to_collect_more;
 }
 
 
 int Heap::NotifyContextDisposed(bool dependant_context) {
   if (!dependant_context) {
     tracer()->ResetSurvivalEvents();
     old_generation_size_configured_ = false;
     MemoryReducer::Event event;
-    event.type = MemoryReducer::kContextDisposed;
+    event.type = MemoryReducer::kPossibleGarbage;
     event.time_ms = MonotonicallyIncreasingTimeInMs();
-    memory_reducer_->NotifyContextDisposed(event);
+    memory_reducer_->NotifyPossibleGarbage(event);
   }
   if (isolate()->concurrent_recompilation_enabled()) {
     // Flush the queued recompilation tasks.
     isolate()->optimizing_compile_dispatcher()->Flush();
   }
   AgeInlineCaches();
   number_of_disposed_maps_ = retained_maps()->Length();
   tracer()->AddContextDisposalTime(MonotonicallyIncreasingTimeInMs());
   return ++contexts_disposed_;
 }
@@ skipping 3029 matching lines @@
 }
 
 
 bool Heap::HasHighFragmentation(intptr_t used, intptr_t committed) {
   const intptr_t kSlack = 16 * MB;
   // Fragmentation is high if committed > 2 * used + kSlack.
   // Rewrite the exression to avoid overflow.
   return committed - used > used + kSlack;
 }
 
+void Heap::SetOptimizeForMemoryUsage() {
+  // 2 pages for each old generation space + 1 page for new space.

[jochen (gone - plz use gerrit), 2016/02/22 09:40:09]

that's lo_space and old_space and?

[ulan, 2016/02/22 10:05:32]

Expanded the comment. It is old, code, and map space. For small heaps lo space
should be close to 0.

+  const int kMinCommittedMemory = 7 * Page::kPageSize;
+  if (ms_count_ == 0 && CommittedMemory() > kMinCommittedMemory) {

[jochen (gone - plz use gerrit), 2016/02/22 09:40:09]

I guess this method is invoked every time a tab goes to the background?

[ulan, 2016/02/22 10:05:32]

yes

+    MemoryReducer::Event event;
+    event.type = MemoryReducer::kPossibleGarbage;
+    event.time_ms = MonotonicallyIncreasingTimeInMs();
+    memory_reducer_->NotifyPossibleGarbage(event);
+  }
+  optimize_for_memory_usage_ = true;
+}
 
 void Heap::ReduceNewSpaceSize() {
   // TODO(ulan): Unify this constant with the similar constant in
   // GCIdleTimeHandler once the change is merged to 4.5.
   static const size_t kLowAllocationThroughput = 1000;
   const size_t allocation_throughput =
       tracer()->CurrentAllocationThroughputInBytesPerMillisecond();
 
   if (FLAG_predictable) return;
 
@@ skipping 2160 matching lines @@
 }
 
 
 // static
 int Heap::GetStaticVisitorIdForMap(Map* map) {
   return StaticVisitorBase::GetVisitorId(map);
 }
 
 }  // namespace internal
 }  // namespace v8