Revert of [heap] Add more tasks for parallel compaction

src/heap/mark-compact.cc

Index: src/heap/mark-compact.cc
diff --git a/src/heap/mark-compact.cc b/src/heap/mark-compact.cc
index 7e6fc61f7c86de7f464f1dfa4dad5d0de6bcd486..7f98b33ec508509c858f20078a5548009ed9d941 100644
--- a/src/heap/mark-compact.cc
+++ b/src/heap/mark-compact.cc
@@ -6,7 +6,6 @@
 
 #include "src/base/atomicops.h"
 #include "src/base/bits.h"
-#include "src/base/sys-info.h"
 #include "src/code-stubs.h"
 #include "src/compilation-cache.h"
 #include "src/cpu-profiler.h"
@@ -3368,39 +3367,26 @@
 }
 
 
-int MarkCompactCollector::NumberOfParallelCompactionTasks() {
-  if (!FLAG_parallel_compaction) return 1;
-  // We cap the number of parallel compaction tasks by
-  // - (#cores - 1)
-  // - a value depending on the list of evacuation candidates
-  // - a hard limit
-  const int kPagesPerCompactionTask = 4;
-  const int kMaxCompactionTasks = 8;
-  return Min(kMaxCompactionTasks,
-             Min(1 + evacuation_candidates_.length() / kPagesPerCompactionTask,
-                 Max(1, base::SysInfo::NumberOfProcessors() - 1)));
-}
-
-
 void MarkCompactCollector::EvacuatePagesInParallel() {
   if (evacuation_candidates_.length() == 0) return;
 
-  const int num_tasks = NumberOfParallelCompactionTasks();
+  int num_tasks = 1;
+  if (FLAG_parallel_compaction) {
+    num_tasks = NumberOfParallelCompactionTasks();
+  }
 
   // Set up compaction spaces.
   CompactionSpaceCollection** compaction_spaces_for_tasks =
       new CompactionSpaceCollection*[num_tasks];
-  FreeList** free_lists = new FreeList*[2 * num_tasks];
   for (int i = 0; i < num_tasks; i++) {
     compaction_spaces_for_tasks[i] = new CompactionSpaceCollection(heap());
-    free_lists[i] = compaction_spaces_for_tasks[i]->Get(OLD_SPACE)->free_list();
-    free_lists[i + num_tasks] =
-        compaction_spaces_for_tasks[i]->Get(CODE_SPACE)->free_list();
-  }
-  heap()->old_space()->DivideFreeLists(free_lists, num_tasks, 1 * MB);
-  heap()->code_space()->DivideFreeLists(&free_lists[num_tasks], num_tasks,
-                                        1 * MB);
-  delete[] free_lists;
+  }
+
+  compaction_spaces_for_tasks[0]->Get(OLD_SPACE)->MoveOverFreeMemory(
+      heap()->old_space());
+  compaction_spaces_for_tasks[0]
+      ->Get(CODE_SPACE)
+      ->MoveOverFreeMemory(heap()->code_space());
 
   compaction_in_progress_ = true;
   // Kick off parallel tasks.
@@ -3411,8 +3397,10 @@
         v8::Platform::kShortRunningTask);
   }
 
-  // Perform compaction on the main thread.
+  // Contribute in main thread. Counter and signal are in principal not needed.
+  concurrent_compaction_tasks_active_++;
   EvacuatePages(compaction_spaces_for_tasks[0], &migration_slots_buffer_);
+  pending_compaction_tasks_semaphore_.Signal();
 
   WaitUntilCompactionCompleted();