Tweak compaction candidate selection to avoid keeping page with low occupancy around.

src/profile-generator.cc

Index: src/profile-generator.cc
diff --git a/src/profile-generator.cc b/src/profile-generator.cc
index 409c24cc61f755fc0d47cfbd1607445883a7aea5..d2f860443371ef1f302b4178c80276b74bd2df3a 100644
--- a/src/profile-generator.cc
+++ b/src/profile-generator.cc
@@ -1562,7 +1562,8 @@ void HeapSnapshotsCollection::RemoveSnapshot(HeapSnapshot* snapshot) {
 
 Handle<HeapObject> HeapSnapshotsCollection::FindHeapObjectById(uint64_t id) {
   // First perform a full GC in order to avoid dead objects.
-  HEAP->CollectAllGarbage(Heap::kMakeHeapIterableMask);
+  HEAP->CollectAllGarbage(Heap::kMakeHeapIterableMask,
+                          "HeapSnapshotsCollection::FindHeapObjectById");
   AssertNoAllocation no_allocation;
   HeapObject* object = NULL;
   HeapIterator iterator(HeapIterator::kFilterUnreachable);
@@ -3048,8 +3049,12 @@ bool HeapSnapshotGenerator::GenerateSnapshot() {
   // full GC is reachable from the root when computing dominators.
   // This is not true for weakly reachable objects.
   // As a temporary solution we call GC twice.
-  Isolate::Current()->heap()->CollectAllGarbage(Heap::kMakeHeapIterableMask);
-  Isolate::Current()->heap()->CollectAllGarbage(Heap::kMakeHeapIterableMask);
+  Isolate::Current()->heap()->CollectAllGarbage(
+      Heap::kMakeHeapIterableMask,
+      "HeapSnapshotGenerator::GenerateSnapshot");
+  Isolate::Current()->heap()->CollectAllGarbage(
+      Heap::kMakeHeapIterableMask,
+      "HeapSnapshotGenerator::GenerateSnapshot");
 
 #ifdef DEBUG
   Heap* debug_heap = Isolate::Current()->heap();