[heap,snapshot] Replace first page size from snapshots with page trimming

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 <utility>
 
 #include "src/base/bits.h"
 #include "src/base/platform/platform.h"
@@ skipping 598 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 127 matching lines @@
   return MemoryChunk::Initialize(heap, base, chunk_size, area_start, area_end,
                                  executable, owner, &reservation);
 }
 
 
 void Page::ResetFreeListStatistics() {
   wasted_memory_ = 0;
   available_in_free_list_ = 0;
 }
 
+size_t Page::ShrinkToHighWaterMark() {
+  // Shrink pages to high water mark. The water mark points either to a filler
+  // or the area_end.
+  HeapObject* filler = HeapObject::FromAddress(HighWaterMark());
+  if (filler->address() == area_end()) return 0;
+  CHECK(filler->IsFiller());
+  if (!filler->IsFreeSpace()) return 0;
+
+#ifdef DEBUG
+  // Check the the filler is indeed the last filler on the page.
+  HeapObjectIterator it(this);
+  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() == area_end()) return 0;
+  DCHECK(filler2->IsFiller());
+  DCHECK_EQ(filler->address(), filler2->address());
+#endif  // DEBUG
+
+  size_t unused = RoundDown(
+      static_cast<size_t>(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*>(this),
+                   reinterpret_cast<void*>(area_end()),
+                   reinterpret_cast<void*>(area_end() - unused));
+    }
+    heap()->CreateFillerObjectAt(
+        filler->address(),
+        static_cast<int>(area_end() - filler->address() - unused),
+        ClearRecordedSlots::kNo);
+    heap()->memory_allocator()->ShrinkChunk(this, unused);
+    CHECK(filler->IsFiller());
+    CHECK_EQ(filler->address() + filler->Size(), area_end());
+  }
+  return unused;
+}
+
 void MemoryAllocator::PartialFreeMemory(MemoryChunk* chunk,
                                         Address start_free) {
   // We do not allow partial shrink for code.
   DCHECK(chunk->executable() == NOT_EXECUTABLE);
 
   intptr_t size;
   base::VirtualMemory* reservation = chunk->reserved_memory();
   DCHECK(reservation->IsReserved());
   size = static_cast<intptr_t>(reservation->size());
 
@@ skipping 451 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() {
+  DCHECK(!heap()->deserialization_complete());
+  MemoryChunk::UpdateHighWaterMark(allocation_info_.top());
+  EmptyAllocationInfo();
+  ResetFreeList();
+
+  for (Page* page : *this) {
+    DCHECK(page->IsFlagSet(Page::NEVER_EVACUATE));
+    size_t unused = page->ShrinkToHighWaterMark();
+    accounting_stats_.DecreaseCapacity(static_cast<intptr_t>(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();
@@ skipping 76 matching lines @@
   SetTopAndLimit(NULL, NULL);
   Free(current_top, static_cast<int>(current_limit - current_top));
 }
 
 void PagedSpace::IncreaseCapacity(size_t bytes) {
   accounting_stats_.ExpandSpace(bytes);
 }
 
 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));
 
   page->ReleaseBlackAreaEndMarkerMap();
 
   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