[heap] Reland uncommit unused large object page memory.

src/heap/spaces.cc

Index: src/heap/spaces.cc
diff --git a/src/heap/spaces.cc b/src/heap/spaces.cc
index 6b47c95bb086bd3af66f83ab552bfe5f7e0146d6..727c4e210333247d537365c679912133f84c9b77 100644
--- a/src/heap/spaces.cc
+++ b/src/heap/spaces.cc
@@ -570,6 +570,11 @@ bool MemoryChunk::CommitArea(size_t requested) {
   return true;
 }
 
+size_t MemoryChunk::CommittedPhysicalMemory() {
+  if (!base::VirtualMemory::HasLazyCommits() || owner()->identity() == LO_SPACE)
+    return size();
+  return high_water_mark_.Value();
+}
 
 void MemoryChunk::InsertAfter(MemoryChunk* other) {
   MemoryChunk* other_next = other->next_chunk();
@@ -737,6 +742,27 @@ void Page::ResetFreeListStatistics() {
   available_in_free_list_ = 0;
 }
 
+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());
+
+  size_t to_free_size = size - (start_free - chunk->address());
+
+  DCHECK(size_.Value() >= static_cast<intptr_t>(to_free_size));
+  size_.Increment(-static_cast<intptr_t>(to_free_size));
+  isolate_->counters()->memory_allocated()->Decrement(
+      static_cast<int>(to_free_size));
+  chunk->set_size(size - to_free_size);
+
+  reservation->ReleasePartial(start_free);
+}
+
 void MemoryAllocator::PreFreeMemory(MemoryChunk* chunk) {
   DCHECK(!chunk->IsFlagSet(MemoryChunk::PRE_FREED));
   LOG(isolate_, DeleteEvent("MemoryChunk", chunk));
@@ -2908,6 +2934,31 @@ void PagedSpace::ResetCodeAndMetadataStatistics(Isolate* isolate) {
 void MapSpace::VerifyObject(HeapObject* object) { CHECK(object->IsMap()); }
 #endif
 
+Address LargePage::GetAddressToShrink() {
+  HeapObject* object = GetObject();
+  if (executable() == EXECUTABLE) {
+    return 0;
+  }
+  size_t used_size = RoundUp((object->address() - address()) + object->Size(),
+                             base::OS::CommitPageSize());
+  if (used_size < CommittedPhysicalMemory()) {
+    return address() + used_size;
+  }
+  return 0;
+}
+
+void LargePage::ClearOutOfLiveRangeSlots(Address free_start) {
+  if (old_to_new_slots() != nullptr) {
+    old_to_new_slots()->RemoveRange(
+        static_cast<int>(free_start - address()),
+        static_cast<int>(free_start + size() - address()));
+  }
+  if (old_to_old_slots() != nullptr) {
+    old_to_old_slots()->RemoveRange(
+        static_cast<int>(free_start - address()),
+        static_cast<int>(free_start + size() - address()));
+  }
+}
 
 // -----------------------------------------------------------------------------
 // LargeObjectIterator
@@ -2981,16 +3032,7 @@ AllocationResult LargeObjectSpace::AllocateRaw(int object_size,
   page->set_next_page(first_page_);
   first_page_ = page;
 
-  // Register all MemoryChunk::kAlignment-aligned chunks covered by
-  // this large page in the chunk map.
-  uintptr_t base = reinterpret_cast<uintptr_t>(page) / MemoryChunk::kAlignment;
-  uintptr_t limit = base + (page->size() - 1) / MemoryChunk::kAlignment;
-  for (uintptr_t key = base; key <= limit; key++) {
-    base::HashMap::Entry* entry = chunk_map_.LookupOrInsert(
-        reinterpret_cast<void*>(key), static_cast<uint32_t>(key));
-    DCHECK(entry != NULL);
-    entry->value = page;
-  }
+  InsertChunkMapEntries(page);
 
   HeapObject* object = page->GetObject();
   MSAN_ALLOCATED_UNINITIALIZED_MEMORY(object->address(), object_size);
@@ -3056,6 +3098,33 @@ void LargeObjectSpace::ClearMarkingStateOfLiveObjects() {
   }
 }
 
+void LargeObjectSpace::InsertChunkMapEntries(LargePage* page) {
+  // Register all MemoryChunk::kAlignment-aligned chunks covered by
+  // this large page in the chunk map.
+  uintptr_t start = reinterpret_cast<uintptr_t>(page) / MemoryChunk::kAlignment;
+  uintptr_t limit = start + (page->size() - 1) / MemoryChunk::kAlignment;
+  for (uintptr_t key = start; key <= limit; key++) {
+    base::HashMap::Entry* entry = chunk_map_.InsertNew(
+        reinterpret_cast<void*>(key), static_cast<uint32_t>(key));
+    DCHECK(entry != NULL);
+    entry->value = page;
+  }
+}
+
+void LargeObjectSpace::RemoveChunkMapEntries(LargePage* page) {
+  RemoveChunkMapEntries(page, page->address());
+}
+
+void LargeObjectSpace::RemoveChunkMapEntries(LargePage* page,
+                                             Address free_start) {
+  uintptr_t start = RoundUp(reinterpret_cast<uintptr_t>(free_start),
+                            MemoryChunk::kAlignment) /
+                    MemoryChunk::kAlignment;
+  uintptr_t limit = start + (page->size() - 1) / MemoryChunk::kAlignment;
+  for (uintptr_t key = start; key <= limit; key++) {
+    chunk_map_.Remove(reinterpret_cast<void*>(key), static_cast<uint32_t>(key));
+  }
+}
 
 void LargeObjectSpace::FreeUnmarkedObjects() {
   LargePage* previous = NULL;
@@ -3065,6 +3134,13 @@ void LargeObjectSpace::FreeUnmarkedObjects() {
     MarkBit mark_bit = Marking::MarkBitFrom(object);
     DCHECK(!Marking::IsGrey(mark_bit));
     if (Marking::IsBlack(mark_bit)) {
+      Address free_start;
+      if ((free_start = current->GetAddressToShrink()) != 0) {
+        // TODO(hpayer): Perform partial free concurrently.
+        current->ClearOutOfLiveRangeSlots(free_start);
+        RemoveChunkMapEntries(current, free_start);
+        heap()->memory_allocator()->PartialFreeMemory(current, free_start);
+      }
       previous = current;
       current = current->next_page();
     } else {
@@ -3083,17 +3159,7 @@ void LargeObjectSpace::FreeUnmarkedObjects() {
       objects_size_ -= object->Size();
       page_count_--;
 
-      // Remove entries belonging to this page.
-      // Use variable alignment to help pass length check (<= 80 characters)
-      // of single line in tools/presubmit.py.
-      const intptr_t alignment = MemoryChunk::kAlignment;
-      uintptr_t base = reinterpret_cast<uintptr_t>(page) / alignment;
-      uintptr_t limit = base + (page->size() - 1) / alignment;
-      for (uintptr_t key = base; key <= limit; key++) {
-        chunk_map_.Remove(reinterpret_cast<void*>(key),
-                          static_cast<uint32_t>(key));
-      }
-
+      RemoveChunkMapEntries(page);
       heap()->memory_allocator()->Free<MemoryAllocator::kPreFreeAndQueue>(page);
     }
   }