Store segment size in SHSegmentInfo

include/hermes/VM/CardTableNC.h

@@ -63,11 +63,9 @@ class CardTable {
   static constexpr size_t kCardSize = 1 << kLogCardSize; // ==> 512-byte cards.
   static constexpr size_t kSegmentSize = 1 << HERMESVM_LOG_HEAP_SEGMENT_SIZE;
 
-  /// The number of valid indices into the card table.
-  static constexpr size_t kValidIndices = kSegmentSize >> kLogCardSize;
-
-  /// The size of the card table.
-  static constexpr size_t kCardTableSize = kValidIndices;
+  /// The size of the maximum inline card table. CardStatus array and boundary
+  /// array for larger segment has larger size and is stored separately.
+  static constexpr size_t kInlineCardTableSize = kSegmentSize >> kLogCardSize;
 
   /// For convenience, this is a conversion factor to determine how many bytes
   /// in the heap correspond to a single byte in the card table. This is
@@ -77,23 +75,31 @@ class CardTable {
   /// guaranteed by a static_assert below.
   static constexpr size_t kHeapBytesPerCardByte = kCardSize;
 
-  /// A prefix of every segment is occupied by auxilary data
-  /// structures.  The card table is the first such data structure.
-  /// The card table maps to the segment.  Only the suffix of the card
-  /// table that maps to the suffix of entire segment that is used for
-  /// allocation is ever used; the prefix that maps to the card table
-  /// itself is not used.  (Nor is the portion that of the card table
-  /// that maps to the other auxiliary data structure, the mark bit
-  /// array, but we don't attempt to calculate that here.)
-  /// It is useful to know the size of this unused region of
-  /// the card table, so it can be used for other purposes.
-  /// Note that the total size of the card table is 2 times
-  /// kCardTableSize, since the CardTable contains two byte arrays of
-  /// that size (cards_ and _boundaries_).
-  static constexpr size_t kFirstUsedIndex =
-      (2 * kCardTableSize) >> kLogCardSize;
-
-  CardTable() = default;
+  /// A prefix of every segment is occupied by auxiliary data structures. The
+  /// card table is the first such data structure. The card table maps to the
+  /// segment. Only the suffix of the card table that maps to the suffix of
+  /// entire segment that is used for allocation is ever used; the prefix that
+  /// maps to the card table itself is not used, nor is the portion of the card
+  /// table that maps to the other auxiliary data structure: the mark bit array
+  /// and guard pages. This small space can be used for other purpose, such as
+  /// storing the SHSegmentInfo (we assert in AlignedHeapSegment that its size
+  /// won't exceed this unused space). The actual first used index should take
+  /// into account all these structures. Here we only calculate for CardTable
+  /// and size of SHSegmentInfo. It's only used as starting index for
+  /// clearing/dirtying range of bits.
+  /// Note that the total size of the card table is 2 times kCardTableSize,
+  /// since the CardTable contains two byte arrays of that size (cards_ and
+  /// boundaries_). And this index must be larger than the size of SHSegmentInfo
+  /// to avoid corrupting it when clearing/dirtying bits.
+  static constexpr size_t kFirstUsedIndex = std::max(
+      sizeof(SHSegmentInfo),
+      (2 * kInlineCardTableSize) >> kLogCardSize);
+
+  CardTable() {
+    // Preserve the segment size.
+    segmentInfo_.shiftedSegmentSize =
+        kSegmentSize >> HERMESVM_LOG_HEAP_SEGMENT_SIZE;
+  }
   /// CardTable is not copyable or movable: It must be constructed in-place.
   CardTable(const CardTable &) = delete;
   CardTable(CardTable &&) = delete;
@@ -184,6 +190,18 @@ class CardTable {
   /// is the first object.)
   GCCell *firstObjForCard(unsigned index) const;
 
+  /// Get the segment size from SHSegmentInfo. This is only used in debug code
+  /// or when clearing the entire card table.
+  size_t getSegmentSize() const {
+    return (size_t)segmentInfo_.shiftedSegmentSize
+        << HERMESVM_LOG_HEAP_SEGMENT_SIZE;
+  }
+
+  /// The end index of the card table (all valid indices should be smaller).
+  size_t getEndIndex() const {
+    return getSegmentSize() >> kLogCardSize;
+  }
+
 #ifdef HERMES_EXTRA_DEBUG
   /// Temporary debugging hack: yield the numeric value of the boundaries_ array
   /// for the given \p index.
@@ -215,9 +233,11 @@ class CardTable {
 
  private:
 #ifndef NDEBUG
-  /// Returns the pointer to the end of the storage containing \p ptr
-  /// (exclusive).
-  static void *storageEnd(const void *ptr);
+  /// Returns the pointer to the end of the storage starting at \p lowLim.
+  void *storageEnd(const void *lowLim) const {
+    return reinterpret_cast<char *>(
+        reinterpret_cast<uintptr_t>(lowLim) + getSegmentSize());
+  }
 #endif
 
   enum class CardStatus : char { Clean = 0, Dirty = 1 };
@@ -255,9 +275,14 @@ class CardTable {
 
   void cleanOrDirtyRange(size_t from, size_t to, CardStatus cleanOrDirty);
 
-  /// This needs to be atomic so that the background thread in Hades can safely
-  /// dirty cards when compacting.
-  std::array<AtomicIfConcurrentGC<CardStatus>, kCardTableSize> cards_{};
+  union {
+    /// The bytes occupied by segmentInfo_ are guaranteed to be not override by
+    /// writes to cards_ array. See static assertions in AlignedHeapSegmentBase.
+    SHSegmentInfo segmentInfo_;
+    /// This needs to be atomic so that the background thread in Hades can
+    /// safely dirty cards when compacting.
+    std::array<AtomicIfConcurrentGC<CardStatus>, kInlineCardTableSize> cards_{};
+  };
 
   /// See the comment at kHeapBytesPerCardByte above to see why this is
   /// necessary.
@@ -275,7 +300,7 @@ class CardTable {
   /// time:  If we allocate a large object that crosses many cards, the first
   /// crossed cards gets a non-negative value, and each subsequent one uses the
   /// maximum exponent that stays within the card range for the object.
-  int8_t boundaries_[kCardTableSize];
+  int8_t boundaries_[kInlineCardTableSize];
 };
 
 /// Implementations of inlines.
@@ -305,7 +330,7 @@ inline size_t CardTable::addressToIndex(const void *addr) const {
 }
 
 inline const char *CardTable::indexToAddress(size_t index) const {
-  assert(index <= kValidIndices && "index must be within the index range");
+  assert(index <= getEndIndex() && "index must be within the index range");
   const char *res = base() + (index << kLogCardSize);
   assert(
       base() <= res && res <= storageEnd(base()) &&
@@ -323,7 +348,7 @@ inline bool CardTable::isCardForAddressDirty(const void *addr) const {
 }
 
 inline bool CardTable::isCardForIndexDirty(size_t index) const {
-  assert(index < kValidIndices && "index is required to be in range.");
+  assert(index < getEndIndex() && "index is required to be in range.");
   return cards_[index].load(std::memory_order_relaxed) == CardStatus::Dirty;
 }
 

include/hermes/VM/HeapRuntime.h

@@ -22,7 +22,7 @@ class HeapRuntime {
  public:
   ~HeapRuntime() {
     runtime_->~RT();
-    sp_->deleteStorage(runtime_);
+    sp_->deleteStorage(runtime_, kHeapRuntimeStorageSize);
   }
 
   /// Allocate a segment and create an aliased shared_ptr that points to the
@@ -36,16 +36,17 @@ class HeapRuntime {
 
  private:
   HeapRuntime(std::shared_ptr<StorageProvider> sp) : sp_{std::move(sp)} {
-    auto ptrOrError = sp_->newStorage("hermes-rt");
+    auto ptrOrError = sp_->newStorage("hermes-rt", kHeapRuntimeStorageSize);
     if (!ptrOrError)
       hermes_fatal("Cannot initialize Runtime storage.", ptrOrError.getError());
-    static_assert(
-        sizeof(RT) < AlignedHeapSegment::storageSize(), "Segments too small.");
+    static_assert(sizeof(RT) < kHeapRuntimeStorageSize, "Segments too small.");
     runtime_ = static_cast<RT *>(*ptrOrError);
   }
 
   std::shared_ptr<StorageProvider> sp_;
   RT *runtime_;
+  static constexpr size_t kHeapRuntimeStorageSize =
+      AlignedHeapSegment::storageSize();
 };
 } // namespace vm
 } // namespace hermes

include/hermes/VM/LimitedStorageProvider.h

@@ -29,9 +29,9 @@ class LimitedStorageProvider final : public StorageProvider {
       : delegate_(std::move(provider)), limit_(limit) {}
 
  protected:
-  llvh::ErrorOr<void *> newStorageImpl(const char *name) override;
+  llvh::ErrorOr<void *> newStorageImpl(const char *name, size_t sz) override;
 
-  void deleteStorageImpl(void *storage) override;
+  void deleteStorageImpl(void *storage, size_t sz) override;
 };
 
 } // namespace vm

include/hermes/VM/StorageProvider.h

@@ -37,20 +37,21 @@ class StorageProvider {
 
   /// @}
 
-  /// Create a new segment memory space.
-  llvh::ErrorOr<void *> newStorage() {
-    return newStorage(nullptr);
+  /// Create a new segment memory space with given size \p sz.
+  llvh::ErrorOr<void *> newStorage(size_t sz) {
+    return newStorage(nullptr, sz);
   }
-  /// Create a new segment memory space and give this memory the name \p name.
-  /// \return A pointer to a block of memory that has
-  /// AlignedHeapSegment::storageSize() bytes, and is aligned on
-  /// AlignedHeapSegment::storageSize().
-  llvh::ErrorOr<void *> newStorage(const char *name);
+  /// \return A pointer to a block of memory that has \p sz bytes, and is
+  /// aligned on AlignedHeapSegmentBase::kSegmentUnitSize. Note that \p sz must
+  /// be non-zero and equals to a multiple of
+  /// AlignedHeapSegmentBase::kSegmentUnitSize.
+  llvh::ErrorOr<void *> newStorage(const char *name, size_t sz);
 
   /// Delete the given segment's memory space, and make it available for re-use.
-  /// \post Nothing in the range [storage, storage +
-  /// AlignedHeapSegment::storageSize()) is valid memory to be read or written.
-  void deleteStorage(void *storage);
+  /// Note that \p sz must be the same as used to allocating \p storage.
+  /// \post Nothing in the range [storage, storage + sz) is valid memory to be
+  /// read or written.
+  void deleteStorage(void *storage, size_t sz);
 
   /// The number of storages this provider has allocated in its lifetime.
   size_t numSucceededAllocs() const;
@@ -67,8 +68,8 @@ class StorageProvider {
   size_t numLiveAllocs() const;
 
  protected:
-  virtual llvh::ErrorOr<void *> newStorageImpl(const char *name) = 0;
-  virtual void deleteStorageImpl(void *storage) = 0;
+  virtual llvh::ErrorOr<void *> newStorageImpl(const char *name, size_t sz) = 0;
+  virtual void deleteStorageImpl(void *storage, size_t sz) = 0;
 
  private:
   size_t numSucceededAllocs_{0};

include/hermes/VM/sh_segment_info.h

@@ -12,6 +12,10 @@
 /// contain segment-specific information.
 typedef struct SHSegmentInfo {
   unsigned index;
+  // Every segment is aligned to 1<<HERMESVM_LOG_HEAP_SEGMENT_SIZE, so we only
+  // need to store the bits after a right shift. A two bytes integer is large
+  // enough to hold a 4GB segment.
+  unsigned short shiftedSegmentSize;
 } SHSegmentInfo;
 
 #endif

lib/VM/LimitedStorageProvider.cpp

@@ -13,20 +13,22 @@
 namespace hermes {
 namespace vm {
 
-llvh::ErrorOr<void *> LimitedStorageProvider::newStorageImpl(const char *name) {
+llvh::ErrorOr<void *> LimitedStorageProvider::newStorageImpl(
+    const char *name,
+    size_t sz) {
   if (limit_ < AlignedHeapSegment::storageSize()) {
     return make_error_code(OOMError::TestVMLimitReached);
   }
-  limit_ -= AlignedHeapSegment::storageSize();
-  return delegate_->newStorage(name);
+  limit_ -= sz;
+  return delegate_->newStorage(name, sz);
 }
 
-void LimitedStorageProvider::deleteStorageImpl(void *storage) {
+void LimitedStorageProvider::deleteStorageImpl(void *storage, size_t sz) {
   if (!storage) {
     return;
   }
-  delegate_->deleteStorage(storage);
-  limit_ += AlignedHeapSegment::storageSize();
+  delegate_->deleteStorage(storage, sz);
+  limit_ += sz;
 }
 
 } // namespace vm