[heap] Perform more aggressive compaction when optimizing for memory usage.

src/heap/mark-compact.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/mark-compact.h"
 
 #include "src/base/atomicops.h"
 #include "src/base/bits.h"
 #include "src/base/sys-info.h"
 #include "src/code-stubs.h"
@@ skipping 579 matching lines @@
       UNREACHABLE();
   }
 
   return NULL;
 }
 
 
 void MarkCompactCollector::ComputeEvacuationHeuristics(
     int area_size, int* target_fragmentation_percent,
     int* max_evacuated_bytes) {
-  // For memory reducing mode we directly define both constants.
+  // For memory reducing and optimize for memory mode we directly define both
+  // constants.
   const int kTargetFragmentationPercentForReduceMemory = 20;
   const int kMaxEvacuatedBytesForReduceMemory = 12 * Page::kPageSize;
+  const int kTargetFragmentationPercentForOptimizeMemory = 20;
+  const int kMaxEvacuatedBytesForOptimizeMemory = 6 * MB;
 
   // For regular mode (which is latency critical) we define less aggressive
   // defaults to start and switch to a trace-based (using compaction speed)
   // approach as soon as we have enough samples.
   const int kTargetFragmentationPercent = 70;
   const int kMaxEvacuatedBytes = 4 * Page::kPageSize;
   // Time to take for a single area (=payload of page). Used as soon as there
   // exist enough compaction speed samples.
   const int kTargetMsPerArea = 1;
 
   if (heap()->ShouldReduceMemory()) {
     *target_fragmentation_percent = kTargetFragmentationPercentForReduceMemory;
     *max_evacuated_bytes = kMaxEvacuatedBytesForReduceMemory;
+  } else if (heap()->ShouldOptimizeForMemoryUsage()) {
+    *target_fragmentation_percent =
+        kTargetFragmentationPercentForOptimizeMemory;
+    *max_evacuated_bytes = kMaxEvacuatedBytesForOptimizeMemory;
   } else {
     const double estimated_compaction_speed =
         heap()->tracer()->CompactionSpeedInBytesPerMillisecond();
     if (estimated_compaction_speed != 0) {
       // Estimate the target fragmentation based on traced compaction speed
       // and a goal for a single page.
       const double estimated_ms_per_area =
           1 + area_size / estimated_compaction_speed;
       *target_fragmentation_percent = static_cast<int>(
           100 - 100 * kTargetMsPerArea / estimated_ms_per_area);
@@ skipping 3395 matching lines @@
       // The target is always in old space, we don't have to record the slot in
       // the old-to-new remembered set.
       DCHECK(!heap()->InNewSpace(target));
       RecordRelocSlot(host, &rinfo, target);
     }
   }
 }
 
 }  // namespace internal
 }  // namespace v8