Reduce GC from external allocation.

runtime/vm/scavenger.cc

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/scavenger.h"
 
 #include <algorithm>
 #include <map>
 #include <utility>
 
@@ skipping 693 matching lines @@
   had_promotion_failure_ = false;
   Isolate* isolate = Isolate::Current();
   NoHandleScope no_handles(isolate);
 
   if (FLAG_verify_before_gc) {
     OS::PrintErr("Verifying before Scavenge...");
     heap_->Verify();
     OS::PrintErr(" done.\n");
   }
 
-  // During from/to flip and promoted stack use, move external allocation
-  // out of tospace temporarily.
-  intptr_t saved_external = external_size_;
-  FreeExternal(saved_external);
-
   // Setup the visitor and run a scavenge.
   ScavengerVisitor visitor(isolate, this);
   Prologue(isolate, invoke_api_callbacks);
   const bool prologue_weak_are_strong = !invoke_api_callbacks;
   IterateRoots(isolate, &visitor, prologue_weak_are_strong);
   int64_t start = OS::GetCurrentTimeMicros();
   ProcessToSpace(&visitor);
   int64_t middle = OS::GetCurrentTimeMicros();
   IterateWeakReferences(isolate, &visitor);
-  // Done with promoted stack; restore external allocation.
-  ASSERT(!PromotedStackHasMore());
-  AllocateExternal(saved_external);
   ScavengerWeakVisitor weak_visitor(this, prologue_weak_are_strong);
   // Include the prologue weak handles, since we must process any promotion.
   const bool visit_prologue_weak_handles = true;
   IterateWeakRoots(isolate, &weak_visitor, visit_prologue_weak_handles);
   visitor.Finalize();
   ProcessWeakTables();
   int64_t end = OS::GetCurrentTimeMicros();
   heap_->RecordTime(kProcessToSpace, middle - start);
   heap_->RecordTime(kIterateWeaks, end - middle);
   Epilogue(isolate, &visitor, invoke_api_callbacks);
@@ skipping 26 matching lines @@
   space.AddProperty("used", UsedInWords() * kWordSize);
   space.AddProperty("capacity", CapacityInWords() * kWordSize);
   space.AddProperty("external", ExternalInWords() * kWordSize);
   space.AddProperty("time", MicrosecondsToSeconds(gc_time_micros()));
 }
 
 
 void Scavenger::AllocateExternal(intptr_t size) {
   ASSERT(size >= 0);
   external_size_ += size;
-  intptr_t remaining = end_ - top_;
-  end_ -= Utils::Minimum(remaining, size);
 }
 
 
 void Scavenger::FreeExternal(intptr_t size) {
   ASSERT(size >= 0);
   external_size_ -= size;
   ASSERT(external_size_ >= 0);
-  end_ = Utils::Minimum(to_->end(), end_ + size);
 }
 
 }  // namespace dart