[tracing] Optimize AllocationRegister and increase max backtrace depth.

base/trace_event/heap_profiler_allocation_register.cc

Index: base/trace_event/heap_profiler_allocation_register.cc
diff --git a/base/trace_event/heap_profiler_allocation_register.cc b/base/trace_event/heap_profiler_allocation_register.cc
index a0fc4be282dff9d4ff16cab045ee1056c6a64339..9c0f1001d1026856524d1f42792c38ae73df7c57 100644
--- a/base/trace_event/heap_profiler_allocation_register.cc
+++ b/base/trace_event/heap_profiler_allocation_register.cc
@@ -9,190 +9,144 @@
 namespace base {
 namespace trace_event {
 
+AllocationRegister::ConstIterator::ConstIterator(
+    const AllocationRegister& alloc_register, AllocationKVIndex index)
+    : register_(alloc_register),
+      index_(index) {}
+
+void AllocationRegister::ConstIterator::operator++() {
+  index_ = register_.allocations_.FindValidIndex(index_ + 1);
+}
+
+bool AllocationRegister::ConstIterator::operator!=(
+    const ConstIterator& other) const {
+  return index_ != other.index_;
+}
+
+AllocationRegister::Allocation
+AllocationRegister::ConstIterator::operator*() const {
+  return register_.GetAllocation(index_);
+}
+
+size_t AllocationRegister::AddressHasher::operator () (
+    const void* address) const {
+  // The multiplicative hashing scheme from [Knuth 1998]. The value of |a| has
+  // been chosen carefully based on measurements with real-word data (addresses
+  // recorded from a Chrome trace run). It is the first prime after 2^17. For
+  // |shift|, 13, 14 and 15 yield good results. These values are tuned to 2^18
+  // buckets. Microbenchmarks show that this simple scheme outperforms fancy
+  // hashes like Murmur3 by 20 to 40 percent.
+  const uintptr_t key = reinterpret_cast<uintptr_t>(address);
+  const uintptr_t a = 131101;
+  const uintptr_t shift = 14;
+  const uintptr_t h = (key * a) >> shift;
+  return h;
+}
+
 AllocationRegister::AllocationRegister()
-    : AllocationRegister(kNumBuckets * kNumCellsPerBucket) {}
-
-AllocationRegister::AllocationRegister(uint32_t num_cells)
-    // Reserve enough address space to store |num_cells_| entries if necessary,
-    // with a guard page after it to crash the program when attempting to store
-    // more entries.
-    : num_cells_(num_cells),
-      cells_(static_cast<Cell*>(AllocateVirtualMemory(num_cells_ *
-                                                      sizeof(Cell)))),
-      buckets_(static_cast<CellIndex*>(
-          AllocateVirtualMemory(kNumBuckets * sizeof(CellIndex)))),
-
-      // The free list is empty. The first unused cell is cell 1, because index
-      // 0 is used as list terminator.
-      free_list_(0),
-      next_unused_cell_(1) {}
+    : AllocationRegister(kNumAllocationCells, kNumBacktraceCells) {}
+
+AllocationRegister::AllocationRegister(size_t num_allocation_cells,
+                                       size_t num_backtrace_cells)
+    : allocations_(kNumAllocationBuckets, num_allocation_cells),
+      backtraces_(kNumBacktraceBuckets, num_backtrace_cells) {}
 
 AllocationRegister::~AllocationRegister() {
-  FreeVirtualMemory(buckets_, kNumBuckets * sizeof(CellIndex));
-  FreeVirtualMemory(cells_, num_cells_ * sizeof(Cell));
 }
 
-void AllocationRegister::Insert(void* address,
+void AllocationRegister::Insert(const void* address,
                                 size_t size,
-                                AllocationContext context) {
+                                const AllocationContext& context) {
   DCHECK(address != nullptr);
-  if (size == 0)
+  if (size == 0) {
     return;
-
-  CellIndex* idx_ptr = Lookup(address);
-
-  // If the index is 0, the address is not yet present, so insert it.
-  if (*idx_ptr == 0) {
-    *idx_ptr = GetFreeCell();
-
-    // The address stored in a cell is const as long as it is exposed (via the
-    // iterators or |Get|), but because cells are re-used, a const cast is
-    // required to set it on insert and remove.
-    void* const& allocation_address = cells_[*idx_ptr].allocation.address;
-    const_cast<void*&>(allocation_address) = address;
-    cells_[*idx_ptr].next = 0;
   }
 
-  cells_[*idx_ptr].allocation.size = size;
-  cells_[*idx_ptr].allocation.context = context;
+  AllocationInfo info = {
+      size,
+      context.type_name,
+      InsertBacktrace(context.backtrace)
+  };
+
+  // Try to insert the allocation.
+  auto index_and_flag = allocations_.Insert(address, info);
+  if (!index_and_flag.second) {
+    // |address| is already there - overwrite the allocation info.
+    auto& old_info = allocations_.Get(index_and_flag.first).second;
+    RemoveBacktrace(old_info.backtrace_index);
+    old_info = info;
+  }
 }
 
-void AllocationRegister::Remove(void* address) {
-  // Get a pointer to the index of the cell that stores |address|. The index can
-  // be an element of |buckets_| or the |next| member of a cell.
-  CellIndex* idx_ptr = Lookup(address);
-  CellIndex freed_idx = *idx_ptr;
-
-  // If the index is 0, the address was not there in the first place.
-  if (freed_idx == 0)
+void AllocationRegister::Remove(const void* address) {
+  auto index = allocations_.Find(address);
+  if (index == AllocationMap::kInvalidKVIndex) {
     return;
+  }
 
-  // The cell at the index is now free, remove it from the linked list for
-  // |Hash(address)|.
-  Cell* freed_cell = &cells_[freed_idx];
-  *idx_ptr = freed_cell->next;
-
-  // Put the free cell at the front of the free list.
-  freed_cell->next = free_list_;
-  free_list_ = freed_idx;
-
-  // Reset the address, so that on iteration the free cell is ignored.
-  const_cast<void*&>(freed_cell->allocation.address) = nullptr;
+  const AllocationInfo& info = allocations_.Get(index).second;
+  RemoveBacktrace(info.backtrace_index);
+  allocations_.Remove(index);
 }
 
-AllocationRegister::Allocation* AllocationRegister::Get(void* address) {
-  CellIndex* idx_ptr = Lookup(address);
+bool AllocationRegister::Get(const void* address,
+                             Allocation* out_allocation) const {
+  auto index = allocations_.Find(address);
+  if (index == AllocationMap::kInvalidKVIndex) {
+    return false;
+  }
 
-  // If the index is 0, the address is not present in the table.
-  return *idx_ptr == 0 ? nullptr : &cells_[*idx_ptr].allocation;
+  if (out_allocation) {
+    *out_allocation = GetAllocation(index);
+  }
+  return true;
 }
 
 AllocationRegister::ConstIterator AllocationRegister::begin() const {
-  // Initialize the iterator's index to 0. Cell 0 never stores an entry.
-  ConstIterator iterator(*this, 0);
-  // Incrementing will advance the iterator to the first used cell.
-  ++iterator;
-  return iterator;
+  return ConstIterator(*this, allocations_.FindValidIndex(0));
 }
 
 AllocationRegister::ConstIterator AllocationRegister::end() const {
-  // Cell |next_unused_cell_ - 1| is the last cell that could contain an entry,
-  // so index |next_unused_cell_| is an iterator past the last element, in line
-  // with the STL iterator conventions.
-  return ConstIterator(*this, next_unused_cell_);
+  return ConstIterator(*this, AllocationMap::kInvalidKVIndex);
 }
 
-AllocationRegister::ConstIterator::ConstIterator(
-    const AllocationRegister& alloc_register,
-    CellIndex index)
-    : register_(alloc_register), index_(index) {}
-
-void AllocationRegister::ConstIterator::operator++() {
-  // Find the next cell with a non-null address until all cells that could
-  // possibly be used have been iterated. A null address indicates a free cell.
-  do {
-    index_++;
-  } while (index_ < register_.next_unused_cell_ &&
-           register_.cells_[index_].allocation.address == nullptr);
-}
-
-bool AllocationRegister::ConstIterator::operator!=(
-    const ConstIterator& other) const {
-  return index_ != other.index_;
-}
-
-const AllocationRegister::Allocation& AllocationRegister::ConstIterator::
-operator*() const {
-  return register_.cells_[index_].allocation;
+void AllocationRegister::EstimateTraceMemoryOverhead(
+    TraceEventMemoryOverhead* overhead) const {
+  size_t allocated = sizeof(AllocationRegister);
+  size_t resident = sizeof(AllocationRegister)
+                    + allocations_.EstimateAllocatedDirty()
+                    + backtraces_.EstimateAllocatedDirty();
+  overhead->Add("AllocationRegister", allocated, resident);
 }
 
-AllocationRegister::CellIndex* AllocationRegister::Lookup(void* address) {
-  // The list head is in |buckets_| at the hash offset.
-  CellIndex* idx_ptr = &buckets_[Hash(address)];
-
-  // Chase down the list until the cell that holds |address| is found,
-  // or until the list ends.
-  while (*idx_ptr != 0 && cells_[*idx_ptr].allocation.address != address)
-    idx_ptr = &cells_[*idx_ptr].next;
-
-  return idx_ptr;
+AllocationRegister::BacktraceMap::KVIndex AllocationRegister::InsertBacktrace(
+    const Backtrace& backtrace) {
+  auto index = backtraces_.Insert(backtrace, 0).first;
+  auto& backtrace_and_count = backtraces_.Get(index);
+  backtrace_and_count.second++;
+  return index;
 }
 
-AllocationRegister::CellIndex AllocationRegister::GetFreeCell() {
-  // First try to re-use a cell from the freelist.
-  if (free_list_) {
-    CellIndex idx = free_list_;
-    free_list_ = cells_[idx].next;
-    return idx;
+void AllocationRegister::RemoveBacktrace(BacktraceMap::KVIndex index) {
+  auto& backtrace_and_count = backtraces_.Get(index);
+  if (--backtrace_and_count.second == 0) {
+    // Backtrace is not referenced anymore - remove it.
+    backtraces_.Remove(index);
   }
-
-  // Otherwise pick the next cell that has not been touched before.
-  CellIndex idx = next_unused_cell_;
-  next_unused_cell_++;
-
-  // If the hash table has too little capacity (when too little address space
-  // was reserved for |cells_|), |next_unused_cell_| can be an index outside of
-  // the allocated storage. A guard page is allocated there to crash the
-  // program in that case. There are alternative solutions:
-  // - Deal with it, increase capacity by reallocating |cells_|.
-  // - Refuse to insert and let the caller deal with it.
-  // Because free cells are re-used before accessing fresh cells with a higher
-  // index, and because reserving address space without touching it is cheap,
-  // the simplest solution is to just allocate a humongous chunk of address
-  // space.
-
-  DCHECK_LT(next_unused_cell_, num_cells_ + 1);
-
-  return idx;
-}
-
-// static
-uint32_t AllocationRegister::Hash(void* address) {
-  // The multiplicative hashing scheme from [Knuth 1998]. The value of |a| has
-  // been chosen carefully based on measurements with real-word data (addresses
-  // recorded from a Chrome trace run). It is the first prime after 2^17. For
-  // |shift|, 13, 14 and 15 yield good results. These values are tuned to 2^18
-  // buckets. Microbenchmarks show that this simple scheme outperforms fancy
-  // hashes like Murmur3 by 20 to 40 percent.
-  const uintptr_t key = reinterpret_cast<uintptr_t>(address);
-  const uintptr_t a = 131101;
-  const uintptr_t shift = 14;
-  const uintptr_t h = (key * a) >> shift;
-  return static_cast<uint32_t>(h) & kNumBucketsMask;
 }
 
-void AllocationRegister::EstimateTraceMemoryOverhead(
-    TraceEventMemoryOverhead* overhead) const {
-  // Estimate memory overhead by counting all of the cells that have ever been
-  // touched. Don't report mmapped memory as allocated, because it has not been
-  // allocated by malloc.
-  size_t allocated = sizeof(AllocationRegister);
-  size_t resident = sizeof(AllocationRegister)
-                    // Include size of touched cells (size of |*cells_|).
-                    + sizeof(Cell) * next_unused_cell_
-                    // Size of |*buckets_|.
-                    + sizeof(CellIndex) * kNumBuckets;
-  overhead->Add("AllocationRegister", allocated, resident);
+AllocationRegister::Allocation AllocationRegister::GetAllocation(
+    AllocationMap::KVIndex index) const {
+  const auto& address_and_info = allocations_.Get(index);
+  const auto& backtrace_and_count = backtraces_.Get(
+      address_and_info.second.backtrace_index);
+  return {
+      address_and_info.first,
+      address_and_info.second.size,
+      AllocationContext(
+          backtrace_and_count.first,
+          address_and_info.second.type_name)
+  };
 }
 
 }  // namespace trace_event