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

src/heap/spaces.cc

 // Copyright 2011 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.
 
 #include "src/heap/spaces.h"
 
 #include "src/base/bits.h"
 #include "src/base/platform/platform.h"
 #include "src/base/platform/semaphore.h"
 #include "src/full-codegen/full-codegen.h"
@@ skipping 577 matching lines @@
 
 void MemoryChunk::Unlink() {
   MemoryChunk* next_element = next_chunk();
   MemoryChunk* prev_element = prev_chunk();
   next_element->set_prev_chunk(prev_element);
   prev_element->set_next_chunk(next_element);
   set_prev_chunk(NULL);
   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,
                                             Executability executable,
                                             Space* owner) {
   DCHECK(commit_area_size <= reserve_area_size);
 
   size_t chunk_size;
   Heap* heap = isolate_->heap();
   Address base = NULL;
@@ skipping 598 matching lines @@
   for (HeapObject* obj = it.Next(); obj != NULL; obj = it.Next()) {
     Address cur = obj->address();
     Address next = cur + obj->Size();
     if ((cur <= addr) && (addr < next)) return obj;
   }
 
   UNREACHABLE();
   return Smi::FromInt(0);
 }
 
+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)) continue;
+
+    // In order to shrink the page, we need to find the last filler. Since
+    // a GC could've happened we need to manually traverse the page to find
+    // any free space at the end.
+    HeapObjectIterator it(page);
+    HeapObject* filler = nullptr;
+    for (HeapObject* obj = it.Next(); obj != nullptr; obj = it.Next()) {

[Hannes Payer (out of office), 2016/08/10 21:17:35]

This seems to be pretty costly. Let's discuss this offline.

[Michael Lippautz, 2016/08/11 09:48:10]

As discussed offline: Switch back to using the high water mark.

Since immortal immovable pages are not swept with this patch, we can
safely use the water mark even with intermediate GCs happening. The
only difficulty is accounting, which is different depending on whether
a GC happened, or not.

+      filler = HeapObject::FromAddress(obj->address() + obj->Size());
+    }
+    if (filler == nullptr || filler->address() == page->area_end()) continue;
+    CHECK(filler->IsFiller());
+    if (!filler->IsFreeSpace()) continue;
+
+    size_t unused =
+        RoundDown(static_cast<size_t>(page->area_end() - filler->address() -
+                                      FreeSpace::kSize),
+                  base::OS::CommitPageSize());
+    if (unused > 0) {
+      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());
+      accounting_stats_.DecreaseCapacity(unused);
+      AccountUncommitted(unused);
+    }
+  }
+}
+
 bool PagedSpace::Expand() {
-  int size = AreaSize();
-  if (snapshotable() && !HasPages()) {
-    size = Snapshot::SizeOfFirstPage(heap()->isolate(), identity());
-  }
-
+  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();
 
   DCHECK(Capacity() <= heap()->MaxOldGenerationSize());
 
   p->InsertAfter(anchor_.prev_page());
 
   return true;
@@ skipping 60 matching lines @@
   }
   Free(current_top, old_linear_size);
 }
 
 void PagedSpace::IncreaseCapacity(int size) {
   accounting_stats_.ExpandSpace(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);
   DCHECK(!free_list_.ContainsPageFreeListItems(page));
 
   if (Page::FromAllocationAreaAddress(allocation_info_.top()) == page) {
     allocation_info_.Reset(nullptr, nullptr);
   }
 
   // If page is still in a list, unlink it from that list.
   if (page->next_chunk() != NULL) {
     DCHECK(page->prev_chunk() != NULL);
     page->Unlink();
   }
 
   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
 void PagedSpace::Print() {}
 #endif
 
 #ifdef VERIFY_HEAP
 void PagedSpace::Verify(ObjectVisitor* visitor) {
   bool allocation_pointer_found_in_space =
       (allocation_info_.top() == allocation_info_.limit());
@@ skipping 1794 matching lines @@
     object->ShortPrint();
     PrintF("\n");
   }
   printf(" --------------------------------------\n");
   printf(" Marked: %x, LiveCount: %x\n", mark_size, LiveBytes());
 }
 
 #endif  // DEBUG
 }  // namespace internal
 }  // namespace v8