Make heap size estimation more accurate.

This improves the heap size estimation by not counting lazy swept pages
as completely allocated but use their live bytes counter instead.

R=vegorov@chromium.org
BUG=v8:1893
TEST=cctest/test-heap/TestSizeOfObjects

Review URL: http://codereview.chromium.org/9173001

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@10383 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/mark-compact.cc

@@ -3641,6 +3641,7 @@ void MarkCompactCollector::SweepSpace(PagedSpace* space, SweeperType sweeper) {
         PrintF("Sweeping 0x%" V8PRIxPTR " lazily postponed.\n",
                reinterpret_cast<intptr_t>(p));
       }
+      space->MarkPageForLazySweeping(p);
       continue;
     }
 

src/spaces.cc

@@ -658,7 +658,8 @@ PagedSpace::PagedSpace(Heap* heap,
     : Space(heap, id, executable),
       free_list_(this),
       was_swept_conservatively_(false),
-      first_unswept_page_(Page::FromAddress(NULL)) {
+      first_unswept_page_(Page::FromAddress(NULL)),
+      unswept_free_bytes_(0) {
   max_capacity_ = (RoundDown(max_capacity, Page::kPageSize) / Page::kPageSize)
                   * Page::kObjectAreaSize;
   accounting_stats_.Clear();
@@ -2062,6 +2063,7 @@ void PagedSpace::PrepareForMarkCompact() {
     } while (p != anchor());
   }
   first_unswept_page_ = Page::FromAddress(NULL);
+  unswept_free_bytes_ = 0;
 
   // Clear the free list before a full GC---it will be rebuilt afterward.
   free_list_.Reset();
@@ -2110,6 +2112,7 @@ bool PagedSpace::AdvanceSweeper(intptr_t bytes_to_sweep) {
         PrintF("Sweeping 0x%" V8PRIxPTR " lazily advanced.\n",
                reinterpret_cast<intptr_t>(p));
       }
+      unswept_free_bytes_ -= (Page::kObjectAreaSize - p->LiveBytes());
       freed_bytes += MarkCompactCollector::SweepConservatively(this, p);
     }
     p = next_page;

src/spaces.h

@@ -1469,9 +1469,12 @@ class PagedSpace : public Space {
   // linear allocation area (between top and limit) are also counted here.
   virtual intptr_t Size() { return accounting_stats_.Size(); }
 
-  // As size, but the bytes in the current linear allocation area are not
-  // included.
-  virtual intptr_t SizeOfObjects() { return Size() - (limit() - top()); }
+  // As size, but the bytes in lazily swept pages are estimated and the bytes
+  // in the current linear allocation area are not included.
+  virtual intptr_t SizeOfObjects() {
+    ASSERT(!IsSweepingComplete() || (unswept_free_bytes_ == 0));
+    return Size() - unswept_free_bytes_ - (limit() - top());
+  }
 
   // Wasted bytes in this space.  These are just the bytes that were thrown away
   // due to being too small to use for allocation.  They do not include the
@@ -1479,9 +1482,7 @@ class PagedSpace : public Space {
   virtual intptr_t Waste() { return accounting_stats_.Waste(); }
 
   // Returns the allocation pointer in this space.
-  Address top() {
-    return allocation_info_.top;
-  }
+  Address top() { return allocation_info_.top; }
   Address limit() { return allocation_info_.limit; }
 
   // Allocate the requested number of bytes in the space if possible, return a
@@ -1557,10 +1558,15 @@ class PagedSpace : public Space {
   }
 
   void SetPagesToSweep(Page* first) {
+    ASSERT(unswept_free_bytes_ == 0);
     if (first == &anchor_) first = NULL;
     first_unswept_page_ = first;
   }
 
+  void MarkPageForLazySweeping(Page* p) {
+    unswept_free_bytes_ += (Page::kObjectAreaSize - p->LiveBytes());
+  }
+
   bool AdvanceSweeper(intptr_t bytes_to_sweep);
 
   bool IsSweepingComplete() {
@@ -1647,8 +1653,15 @@ class PagedSpace : public Space {
 
   bool was_swept_conservatively_;
 
+  // The first page to be swept when the lazy sweeper advances. Is set
+  // to NULL when all pages have been swept.
   Page* first_unswept_page_;
 
+  // The number of free bytes which could be reclaimed by advancing the
+  // lazy sweeper.  This is only an estimation because lazy sweeping is
+  // done conservatively.
+  intptr_t unswept_free_bytes_;
+
   // Expands the space by allocating a fixed number of pages. Returns false if
   // it cannot allocate requested number of pages from OS, or if the hard heap
   // size limit has been hit.

test/cctest/test-heap.cc

@@ -1187,6 +1187,43 @@ TEST(TestInternalWeakListsTraverseWithGC) {
 }
 
 
+TEST(TestSizeOfObjects) {
+  v8::V8::Initialize();
+
+  // Get initial heap size after several full GCs, which will stabilize
+  // the heap size and return with sweeping finished completely.
+  HEAP->CollectAllGarbage(Heap::kNoGCFlags);
+  HEAP->CollectAllGarbage(Heap::kNoGCFlags);
+  HEAP->CollectAllGarbage(Heap::kNoGCFlags);
+  HEAP->CollectAllGarbage(Heap::kNoGCFlags);
+  CHECK(HEAP->old_pointer_space()->IsSweepingComplete());
+  intptr_t initial_size = HEAP->SizeOfObjects();
+
+  {
+    // Allocate objects on several different old-space pages so that
+    // lazy sweeping kicks in for subsequent GC runs.
+    AlwaysAllocateScope always_allocate;
+    intptr_t filler_size = FixedArray::SizeFor(8192);
+    for (int i = 1; i <= 100; i++) {
+      HEAP->AllocateFixedArray(8192, TENURED)->ToObjectChecked();
+      CHECK_EQ(initial_size + i * filler_size, HEAP->SizeOfObjects());
+    }
+  }
+
+  // The heap size should go back to initial size after a full GC, even
+  // though sweeping didn't finish yet.
+  HEAP->CollectAllGarbage(Heap::kNoGCFlags);
+  CHECK(!HEAP->old_pointer_space()->IsSweepingComplete());
+  CHECK_EQ(initial_size, HEAP->SizeOfObjects());
+
+  // Advancing the sweeper step-wise should not change the heap size.
+  while (!HEAP->old_pointer_space()->IsSweepingComplete()) {
+    HEAP->old_pointer_space()->AdvanceSweeper(KB);
+    CHECK_EQ(initial_size, HEAP->SizeOfObjects());
+  }
+}
+
+
 TEST(TestSizeOfObjectsVsHeapIteratorPrecision) {
   InitializeVM();
   HEAP->EnsureHeapIsIterable();