- Introduce histograms collecting data about the number of set remembered set

  bits in a page.
Review URL: http://codereview.chromium.org/113819

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@2045 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/heap.cc

@@ -2664,12 +2664,13 @@ void Heap::ZapFromSpace() {
 #endif  // DEBUG
 
 
-void Heap::IterateRSetRange(Address object_start,
-                            Address object_end,
-                            Address rset_start,
-                            ObjectSlotCallback copy_object_func) {
+int Heap::IterateRSetRange(Address object_start,
+                           Address object_end,
+                           Address rset_start,
+                           ObjectSlotCallback copy_object_func) {
   Address object_address = object_start;
   Address rset_address = rset_start;
+  int set_bits_count = 0;
 
   // Loop over all the pointers in [object_start, object_end).
   while (object_address < object_end) {
@@ -2686,6 +2687,7 @@ void Heap::IterateRSetRange(Address object_start,
           // If this pointer does not need to be remembered anymore, clear
           // the remembered set bit.
           if (!Heap::InNewSpace(*object_p)) result_rset &= ~bitmask;
+          set_bits_count++;
         }
         object_address += kPointerSize;
       }
@@ -2699,6 +2701,7 @@ void Heap::IterateRSetRange(Address object_start,
     }
     rset_address += kIntSize;
   }
+  return set_bits_count;
 }
 
 
@@ -2706,11 +2709,20 @@ void Heap::IterateRSet(PagedSpace* space, ObjectSlotCallback copy_object_func) {
   ASSERT(Page::is_rset_in_use());
   ASSERT(space == old_pointer_space_ || space == map_space_);
 
+  static void* paged_rset_histogram = StatsTable::CreateHistogram(
+      "V8.RSetPaged",
+      0,
+      Page::kObjectAreaSize / kPointerSize,
+      30);
+
   PageIterator it(space, PageIterator::PAGES_IN_USE);
   while (it.has_next()) {
     Page* page = it.next();
-    IterateRSetRange(page->ObjectAreaStart(), page->AllocationTop(),
-                     page->RSetStart(), copy_object_func);
+    int count = IterateRSetRange(page->ObjectAreaStart(), page->AllocationTop(),
+                                 page->RSetStart(), copy_object_func);
+    if (paged_rset_histogram != NULL) {
+      StatsTable::AddHistogramSample(paged_rset_histogram, count);
+    }
   }
 }
 

src/heap.h

@@ -667,10 +667,11 @@ class Heap : public AllStatic {
   // Iterates a range of remembered set addresses starting with rset_start
   // corresponding to the range of allocated pointers
   // [object_start, object_end).
-  static void IterateRSetRange(Address object_start,
-                               Address object_end,
-                               Address rset_start,
-                               ObjectSlotCallback copy_object_func);
+  // Returns the number of bits that were set.
+  static int IterateRSetRange(Address object_start,
+                              Address object_end,
+                              Address rset_start,
+                              ObjectSlotCallback copy_object_func);
 
   // Returns whether the object resides in new space.
   static inline bool InNewSpace(Object* object);

src/spaces.cc

@@ -2423,6 +2423,13 @@ void LargeObjectSpace::ClearRSet() {
 void LargeObjectSpace::IterateRSet(ObjectSlotCallback copy_object_func) {
   ASSERT(Page::is_rset_in_use());
 
+  static void* lo_rset_histogram = StatsTable::CreateHistogram(
+      "V8.RSetLO",
+      0,
+      // Keeping this histogram's buckets the same as the paged space histogram.
+      Page::kObjectAreaSize / kPointerSize,
+      30);
+
   LargeObjectIterator it(this);
   while (it.has_next()) {
     // We only have code, sequential strings, or fixed arrays in large
@@ -2433,15 +2440,18 @@ void LargeObjectSpace::IterateRSet(ObjectSlotCallback copy_object_func) {
       // Iterate the normal page remembered set range.
       Page* page = Page::FromAddress(object->address());
       Address object_end = object->address() + object->Size();
-      Heap::IterateRSetRange(page->ObjectAreaStart(),
-                             Min(page->ObjectAreaEnd(), object_end),
-                             page->RSetStart(),
-                             copy_object_func);
+      int count = Heap::IterateRSetRange(page->ObjectAreaStart(),
+                                         Min(page->ObjectAreaEnd(), object_end),
+                                         page->RSetStart(),
+                                         copy_object_func);
 
       // Iterate the extra array elements.
       if (object_end > page->ObjectAreaEnd()) {
-        Heap::IterateRSetRange(page->ObjectAreaEnd(), object_end,
-                               object_end, copy_object_func);
+        count += Heap::IterateRSetRange(page->ObjectAreaEnd(), object_end,
+                                        object_end, copy_object_func);
+      }
+      if (lo_rset_histogram != NULL) {
+        StatsTable::AddHistogramSample(lo_rset_histogram, count);
       }
     }
   }