Do full GC for small heaps in idle time handler.

BUG=407593
LOG=N
R=hpayer@chromium.org

Review URL: https://codereview.chromium.org/563573002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23871 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/heap/gc-idle-time-handler.cc

@@ -80,7 +80,9 @@ GCIdleTimeAction GCIdleTimeHandler::Compute(size_t idle_time_in_ms,
   if (heap_state.incremental_marking_stopped) {
     if (idle_time_in_ms >= EstimateMarkCompactTime(
                                heap_state.size_of_objects,
-                               heap_state.mark_compact_speed_in_bytes_per_ms)) {
+                               heap_state.mark_compact_speed_in_bytes_per_ms) ||
+        (heap_state.size_of_objects < kSmallHeapSize &&
+         heap_state.contexts_disposed > 0)) {
       // If there are no more than two GCs left in this idle round and we are
       // allowed to do a full GC, then make those GCs full in order to compact
       // the code space.

src/heap/gc-idle-time-handler.h

@@ -98,6 +98,10 @@ class GCIdleTimeHandler {
   // Number of scavenges that will trigger start of new idle round.
   static const int kIdleScavengeThreshold;
 
+  // Heap size threshold below which we prefer mark-compact over incremental
+  // step.
+  static const size_t kSmallHeapSize = 2 * kPointerSize * MB;
+
   struct HeapState {
     int contexts_disposed;
     size_t size_of_objects;