Reland of "[heap] Switch to 500k pages"

src/heap/spaces.cc

Index: src/heap/spaces.cc
diff --git a/src/heap/spaces.cc b/src/heap/spaces.cc
index b31aaf3998fd98a370b3a329dcfb992c12f9e112..cfece78201bc6ffc608cba9a72ffb81abeaa4e83 100644
--- a/src/heap/spaces.cc
+++ b/src/heap/spaces.cc
@@ -595,6 +595,21 @@ void MemoryChunk::Unlink() {
   set_next_chunk(NULL);
 }
 
+void MemoryAllocator::ShrinkChunk(MemoryChunk* chunk, size_t bytes_to_shrink) {
+  DCHECK_GE(bytes_to_shrink, static_cast<size_t>(base::OS::CommitPageSize()));
+  DCHECK_EQ(0, bytes_to_shrink % base::OS::CommitPageSize());
+  Address free_start = chunk->area_end_ - bytes_to_shrink;
+  // Don't adjust the size of the page. The area is just uncomitted but not
+  // released.
+  chunk->area_end_ -= bytes_to_shrink;
+  UncommitBlock(free_start, bytes_to_shrink);
+  if (chunk->IsFlagSet(MemoryChunk::IS_EXECUTABLE)) {
+    if (chunk->reservation_.IsReserved())
+      chunk->reservation_.Guard(chunk->area_end_);
+    else
+      base::OS::Guard(chunk->area_end_, base::OS::CommitPageSize());
+  }
+}
 
 MemoryChunk* MemoryAllocator::AllocateChunk(intptr_t reserve_area_size,
                                             intptr_t commit_area_size,
@@ -1213,21 +1228,80 @@ Object* PagedSpace::FindObject(Address addr) {
   return Smi::FromInt(0);
 }
 
-bool PagedSpace::Expand() {
-  int size = AreaSize();
-  if (snapshotable() && !HasPages()) {
-    size = Snapshot::SizeOfFirstPage(heap()->isolate(), identity());
+void PagedSpace::ShrinkImmortalImmovablePages() {
+  MemoryChunk::UpdateHighWaterMark(allocation_info_.top());
+  EmptyAllocationInfo();
+  ResetFreeList();
+
+  for (Page* page : *this) {
+    // Only shrink immortal immovable pages after deserialization.
+    if (!page->IsFlagSet(Page::NEVER_EVACUATE) ||
+        !page->IsFlagSet(Page::NEVER_SWEEP))
+      continue;
+
+    // Shrink pages to high water mark. Since those pages are never swept, there
+    // should be a filler exactly at the high water mark.
+    HeapObject* filler = HeapObject::FromAddress(page->HighWaterMark());
+    if (filler->address() == page->area_end()) continue;
+    CHECK(filler->IsFiller());
+    if (!filler->IsFreeSpace()) continue;
+
+#ifdef DEBUG

[Michael Lippautz, 2016/08/11 09:48:12]

Debug verification useful?

+    // Check the the filler is indeed the last filler on the page.
+    HeapObjectIterator it(page);
+    HeapObject* filler2 = nullptr;
+    for (HeapObject* obj = it.Next(); obj != nullptr; obj = it.Next()) {
+      filler2 = HeapObject::FromAddress(obj->address() + obj->Size());
+    }
+    if (filler2 == nullptr || filler2->address() == page->area_end()) continue;
+    DCHECK(filler2->IsFiller());
+    DCHECK_EQ(filler->address(), filler2->address());
+#endif  // DEBUG
+
+    size_t unused =
+        RoundDown(static_cast<size_t>(page->area_end() - filler->address() -
+                                      FreeSpace::kSize),
+                  base::OS::CommitPageSize());
+    if (unused > 0) {
+      if (FLAG_trace_gc_verbose) {
+        PrintIsolate(heap()->isolate(), "Shrinking page %p: end %p -> %p\n",
+                     reinterpret_cast<void*>(page),
+                     reinterpret_cast<void*>(page->area_end()),
+                     reinterpret_cast<void*>(page->area_end() - unused));
+      }
+      heap()->CreateFillerObjectAt(
+          filler->address(),
+          static_cast<int>(page->area_end() - filler->address() - unused),
+          ClearRecordedSlots::kNo);
+      heap()->memory_allocator()->ShrinkChunk(page, unused);
+      CHECK(filler->IsFiller());
+      CHECK_EQ(filler->address() + filler->Size(), page->area_end());
+      if (heap()->gc_count() > 0) {
+        // Since a GC already happened, the page area has been accounted for
+        // as capacity *and* allocated bytes.
+        accounting_stats_.ShrinkSpace(static_cast<int>(unused));
+      } else {
+        // No GC happened, the page area has only been accounted for as
+        // capacity.
+        accounting_stats_.DecreaseCapacity(static_cast<intptr_t>(unused));
+      }
+      AccountUncommitted(unused);
+    }
   }
+}
 
+bool PagedSpace::Expand() {
+  const int size = AreaSize();
   if (!heap()->CanExpandOldGeneration(size)) return false;
-
   Page* p = heap()->memory_allocator()->AllocatePage(size, this, executable());
   if (p == nullptr) return false;
-
   AccountCommitted(static_cast<intptr_t>(p->size()));
 
   // Pages created during bootstrapping may contain immortal immovable objects.
-  if (!heap()->deserialization_complete()) p->MarkNeverEvacuate();
+  if (!heap()->deserialization_complete()) {
+    p->MarkNeverEvacuate();
+    p->SetFlag(Page::NEVER_SWEEP);
+  }
 
   DCHECK(Capacity() <= heap()->MaxOldGenerationSize());
 
@@ -1304,7 +1378,6 @@ void PagedSpace::IncreaseCapacity(int size) {
 
 void PagedSpace::ReleasePage(Page* page) {
   DCHECK_EQ(page->LiveBytes(), 0);
-  DCHECK_EQ(AreaSize(), page->area_size());
   DCHECK_EQ(page->owner(), this);
 
   free_list_.EvictFreeListItems(page);
@@ -1321,10 +1394,8 @@ void PagedSpace::ReleasePage(Page* page) {
   }
 
   AccountUncommitted(static_cast<intptr_t>(page->size()));
+  accounting_stats_.ShrinkSpace(page->area_size());
   heap()->memory_allocator()->Free<MemoryAllocator::kPreFreeAndQueue>(page);
-
-  DCHECK(Capacity() > 0);
-  accounting_stats_.ShrinkSpace(AreaSize());
 }
 
 #ifdef DEBUG