[heap] Concurrently free empty typed slot set chunks.

BUG=chromium:648568

Review-Url: https://codereview.chromium.org/2352423002
Cr-Commit-Position: refs/heads/master@{#39605}

src/heap/mark-compact.cc

@@ -3865,6 +3865,12 @@ int MarkCompactCollector::Sweeper::ParallelSweepPage(Page* page,
     } else {
       max_freed = RawSweep(page, REBUILD_FREE_LIST, free_space_mode);
     }
+
+    // After finishing sweeping of a page we clean up its remembered set.
+    if (page->typed_old_to_new_slots()) {
+      page->typed_old_to_new_slots()->FreeToBeFreedChunks();
+    }
+
     {
       base::LockGuard<base::Mutex> guard(&mutex_);
       swept_list_[identity].Add(page);

src/heap/remembered-set.cc

@@ -36,7 +36,8 @@ void RememberedSet<direction>::ClearInvalidSlots(Heap* heap) {
             } else {
               return REMOVE_SLOT;
             }
-          });
+          },
+          TypedSlotSet::PREFREE_EMPTY_CHUNKS);
     }
   }
   for (MemoryChunk* chunk : *heap->map_space()) {

src/heap/remembered-set.h

@@ -149,10 +149,13 @@ class RememberedSet {
   static void RemoveRangeTyped(MemoryChunk* page, Address start, Address end) {
     TypedSlotSet* slots = GetTypedSlotSet(page);
     if (slots != nullptr) {
-      slots->Iterate([start, end](SlotType slot_type, Address host_addr,
-                                  Address slot_addr) {
-        return start <= slot_addr && slot_addr < end ? REMOVE_SLOT : KEEP_SLOT;
-      });
+      slots->Iterate(
+          [start, end](SlotType slot_type, Address host_addr,
+                       Address slot_addr) {
+            return start <= slot_addr && slot_addr < end ? REMOVE_SLOT
+                                                         : KEEP_SLOT;
+          },
+          TypedSlotSet::PREFREE_EMPTY_CHUNKS);
     }
   }
 
@@ -173,7 +176,7 @@ class RememberedSet {
   static void IterateTyped(MemoryChunk* chunk, Callback callback) {
     TypedSlotSet* slots = GetTypedSlotSet(chunk);
     if (slots != nullptr) {
-      int new_count = slots->Iterate(callback);
+      int new_count = slots->Iterate(callback, TypedSlotSet::KEEP_EMPTY_CHUNKS);
       if (new_count == 0) {
         ReleaseTypedSlotSet(chunk);
       }

src/heap/slot-set.h

@@ -5,6 +5,8 @@
 #ifndef V8_SLOT_SET_H
 #define V8_SLOT_SET_H
 
+#include <stack>
+
 #include "src/allocation.h"
 #include "src/base/atomic-utils.h"
 #include "src/base/bits.h"
@@ -259,6 +261,8 @@ enum SlotType {
 // typed slots contain V8 internal pointers that are not directly exposed to JS.
 class TypedSlotSet {
  public:
+  enum IterationMode { PREFREE_EMPTY_CHUNKS, KEEP_EMPTY_CHUNKS };
+
   typedef std::pair<SlotType, uint32_t> TypeAndOffset;
 
   struct TypedSlot {
@@ -326,6 +330,10 @@ class TypedSlotSet {
   void Insert(SlotType type, uint32_t host_offset, uint32_t offset) {
     TypedSlot slot(type, host_offset, offset);
     Chunk* top_chunk = chunk_.Value();
+    if (!top_chunk) {
+      top_chunk = new Chunk(nullptr, kInitialBufferSize);
+      chunk_.SetValue(top_chunk);
+    }
     if (!top_chunk->AddSlot(slot)) {
       Chunk* new_top_chunk =
           new Chunk(top_chunk, NextCapacity(top_chunk->capacity.Value()));
@@ -346,13 +354,15 @@ class TypedSlotSet {
   //    else return REMOVE_SLOT;
   // });
   template <typename Callback>
-  int Iterate(Callback callback) {
+  int Iterate(Callback callback, IterationMode mode) {
     STATIC_ASSERT(CLEARED_SLOT < 8);
     Chunk* chunk = chunk_.Value();
+    Chunk* previous = nullptr;
     int new_count = 0;
     while (chunk != nullptr) {
       TypedSlot* buffer = chunk->buffer.Value();
       int count = chunk->count.Value();
+      bool empty = true;
       for (int i = 0; i < count; i++) {
         // Order is important here. We have to read out the slot type last to
         // observe the concurrent removal case consistently.
@@ -363,16 +373,40 @@ class TypedSlotSet {
           Address addr = page_start_ + type_and_offset.second;
           if (callback(type, host_addr, addr) == KEEP_SLOT) {
             new_count++;
+            empty = false;
           } else {
             buffer[i].Clear();
           }
         }
       }
+
+      if (mode == PREFREE_EMPTY_CHUNKS && empty) {
+        // We remove the chunk from the list but let it still point its next
+        // chunk to allow concurrent iteration.
+        if (previous) {
+          previous->next.SetValue(chunk->next.Value());
+        } else {
+          chunk_.SetValue(chunk->next.Value());
+        }
+        base::LockGuard<base::Mutex> guard(&to_be_freed_chunks_mutex_);
+        to_be_freed_chunks_.push(chunk);
+      } else {
+        previous = chunk;
+      }
       chunk = chunk->next.Value();
     }
     return new_count;
   }
 
+  void FreeToBeFreedChunks() {
+    base::LockGuard<base::Mutex> guard(&to_be_freed_chunks_mutex_);
+    while (!to_be_freed_chunks_.empty()) {
+      Chunk* top = to_be_freed_chunks_.top();
+      to_be_freed_chunks_.pop();
+      delete top;
+    }
+  }
+
  private:
   static const int kInitialBufferSize = 100;
   static const int kMaxBufferSize = 16 * KB;
@@ -411,6 +445,8 @@ class TypedSlotSet {
 
   Address page_start_;
   base::AtomicValue<Chunk*> chunk_;
+  base::Mutex to_be_freed_chunks_mutex_;
+  std::stack<Chunk*> to_be_freed_chunks_;
 };
 
 }  // namespace internal

test/unittests/heap/slot-set-unittest.cc

@@ -152,24 +152,29 @@ TEST(TypedSlotSet, Iterate) {
     ++added;
   }
   int iterated = 0;
-  set.Iterate([&iterated, kDelta, kHostDelta](SlotType type, Address host_addr,
-                                              Address addr) {
-    uint32_t i = static_cast<uint32_t>(reinterpret_cast<uintptr_t>(addr));
-    uint32_t j = static_cast<uint32_t>(reinterpret_cast<uintptr_t>(host_addr));
-    EXPECT_EQ(i % CLEARED_SLOT, static_cast<uint32_t>(type));
-    EXPECT_EQ(0, i % kDelta);
-    EXPECT_EQ(0, j % kHostDelta);
-    ++iterated;
-    return i % 2 == 0 ? KEEP_SLOT : REMOVE_SLOT;
-  });
+  set.Iterate(
+      [&iterated, kDelta, kHostDelta](SlotType type, Address host_addr,
+                                      Address addr) {
+        uint32_t i = static_cast<uint32_t>(reinterpret_cast<uintptr_t>(addr));
+        uint32_t j =
+            static_cast<uint32_t>(reinterpret_cast<uintptr_t>(host_addr));
+        EXPECT_EQ(i % CLEARED_SLOT, static_cast<uint32_t>(type));
+        EXPECT_EQ(0, i % kDelta);
+        EXPECT_EQ(0, j % kHostDelta);
+        ++iterated;
+        return i % 2 == 0 ? KEEP_SLOT : REMOVE_SLOT;
+      },
+      TypedSlotSet::KEEP_EMPTY_CHUNKS);
   EXPECT_EQ(added, iterated);
   iterated = 0;
-  set.Iterate([&iterated](SlotType type, Address host_addr, Address addr) {
-    uint32_t i = static_cast<uint32_t>(reinterpret_cast<uintptr_t>(addr));
-    EXPECT_EQ(0, i % 2);
-    ++iterated;
-    return KEEP_SLOT;
-  });
+  set.Iterate(
+      [&iterated](SlotType type, Address host_addr, Address addr) {
+        uint32_t i = static_cast<uint32_t>(reinterpret_cast<uintptr_t>(addr));
+        EXPECT_EQ(0, i % 2);
+        ++iterated;
+        return KEEP_SLOT;
+      },
+      TypedSlotSet::KEEP_EMPTY_CHUNKS);
   EXPECT_EQ(added / 2, iterated);
 }