Fix corner-case in heap size estimation.

Empty but unswept pages could cause the unswept_free_bytes counter to
to be off in case heap gets shrunk and page gets released before it was
swept properly.

R=vegorov@chromium.org
BUG=v8:1893

Review URL: https://chromiumcodereview.appspot.com/9241010

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@10421 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/mark-compact.cc

@@ -3630,6 +3630,9 @@ void MarkCompactCollector::SweepSpace(PagedSpace* space, SweeperType sweeper) {
           PrintF("Sweeping 0x%" V8PRIxPTR " released page.\n",
                  reinterpret_cast<intptr_t>(p));
         }
+        // Adjust unswept free bytes because releasing a page expects said
+        // counter to be accurate for unswept pages.
+        space->IncreaseUnsweptFreeBytes(p);
         space->ReleasePage(p);
         continue;
       }
@@ -3641,7 +3644,7 @@ void MarkCompactCollector::SweepSpace(PagedSpace* space, SweeperType sweeper) {
         PrintF("Sweeping 0x%" V8PRIxPTR " lazily postponed.\n",
                reinterpret_cast<intptr_t>(p));
       }
-      space->MarkPageForLazySweeping(p);
+      space->IncreaseUnsweptFreeBytes(p);
       continue;
     }
 

src/spaces.cc

@@ -765,6 +765,8 @@ void PagedSpace::ReleasePage(Page* page) {
     intptr_t size = free_list_.EvictFreeListItems(page);
     accounting_stats_.AllocateBytes(size);
     ASSERT_EQ(Page::kObjectAreaSize, static_cast<int>(size));
+  } else {
+    DecreaseUnsweptFreeBytes(page);
   }
 
   if (Page::FromAllocationTop(allocation_info_.top) == page) {
@@ -2112,7 +2114,7 @@ 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());
+      DecreaseUnsweptFreeBytes(p);
       freed_bytes += MarkCompactCollector::SweepConservatively(this, p);
     }
     p = next_page;

src/spaces.h

@@ -1563,10 +1563,16 @@ class PagedSpace : public Space {
     first_unswept_page_ = first;
   }
 
-  void MarkPageForLazySweeping(Page* p) {
+  void IncreaseUnsweptFreeBytes(Page* p) {
+    ASSERT(ShouldBeSweptLazily(p));
     unswept_free_bytes_ += (Page::kObjectAreaSize - p->LiveBytes());
   }
 
+  void DecreaseUnsweptFreeBytes(Page* p) {
+    ASSERT(ShouldBeSweptLazily(p));
+    unswept_free_bytes_ -= (Page::kObjectAreaSize - p->LiveBytes());
+  }
+
   bool AdvanceSweeper(intptr_t bytes_to_sweep);
 
   bool IsSweepingComplete() {