[heap] Add more tasks for parallel compaction

src/heap/mark-compact.h

 // 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.
 
 #ifndef V8_HEAP_MARK_COMPACT_H_
 #define V8_HEAP_MARK_COMPACT_H_
 
 #include "src/base/bits.h"
+#include "src/base/sys-info.h"
 #include "src/heap/spaces.h"
 
 namespace v8 {
 namespace internal {
 
 // Callback function, returns whether an object is alive. The heap size
 // of the object is returned in size. It optionally updates the offset
 // to the first live object in the page (only used for old and map objects).
 typedef bool (*IsAliveFunction)(HeapObject* obj, int* size, int* offset);
 
@@ skipping 683 matching lines @@
                                    SlotsBuffer** evacuation_slots_buffer);
 
   void AddEvacuationSlotsBufferSynchronized(
       SlotsBuffer* evacuation_slots_buffer);
 
   void EvacuatePages(CompactionSpaceCollection* compaction_spaces,
                      SlotsBuffer** evacuation_slots_buffer);
 
   void EvacuatePagesInParallel();
 
+  // The number of parallel compaction tasks, including the main thread.
   int NumberOfParallelCompactionTasks() {

[Hannes Payer (out of office), 2015/09/23 07:26:03]

Implement this in the cc file. That makes it faster to recompile when playing
with this metric. The include can then also move to the cc file.

[Michael Lippautz, 2015/09/23 07:40:50]

Done.

-    // TODO(hpayer, mlippautz): Figure out some logic to determine the number
-    // of compaction tasks.
-    return 1;
+    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

[Hannes Payer (out of office), 2015/09/23 07:26:03]

Make the magic limits named constants.

[Michael Lippautz, 2015/09/23 07:40:50]

Done.

+    return Min(8, Min(1 + evacuation_candidates_.length() / 4,
+                      Max(1, base::SysInfo::NumberOfProcessors() - 1)));
   }
 
   void WaitUntilCompactionCompleted();
 
   void EvacuateNewSpaceAndCandidates();
 
   void ReleaseEvacuationCandidates();
 
   // Moves the pages of the evacuation_candidates_ list to the end of their
   // corresponding space pages list.
@@ skipping 124 matching lines @@
  private:
   MarkCompactCollector* collector_;
 };
 
 
 const char* AllocationSpaceName(AllocationSpace space);
 }
 }  // namespace v8::internal
 
 #endif  // V8_HEAP_MARK_COMPACT_H_