Index: base/trace_event/memory_profiler_allocation_register.cc |
diff --git a/base/trace_event/memory_profiler_allocation_register.cc b/base/trace_event/memory_profiler_allocation_register.cc |
new file mode 100644 |
index 0000000000000000000000000000000000000000..662e86fc0df7a6e2f09507b56ab6795b076d9332 |
--- /dev/null |
+++ b/base/trace_event/memory_profiler_allocation_register.cc |
@@ -0,0 +1,166 @@ |
+// Copyright 2015 The Chromium 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 "base/trace_event/memory_profiler_allocation_register.h" |
+ |
+namespace base { |
+namespace trace_event { |
+ |
+AllocationRegister::AllocationRegister() |
+ // Reserve enough address space to store |kNumCells| entries if necessary, |
+ // with a guard page after it to crash the program when attempting to store |
+ // more entries. |
+ : cells_(static_cast<Cell*>(AllocateVirtualMemory(kNumCells * |
+ 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::~AllocationRegister() { |
+ FreeVirtualMemory(buckets_, kNumBuckets * sizeof(CellIndex)); |
+ FreeVirtualMemory(cells_, kNumCells * sizeof(Cell)); |
+} |
+ |
+void AllocationRegister::Insert(void* address, |
+ size_t size, |
+ AllocationContext context) { |
+ DCHECK(address != nullptr); |
+ |
+ 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(); |
+ |
+ cells_[*idx_ptr].allocation.address = address; |
+ cells_[*idx_ptr].next = 0; |
+ } |
+ |
+ cells_[*idx_ptr].allocation.size = size; |
+ cells_[*idx_ptr].allocation.context = context; |
+} |
+ |
+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) |
+ 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. |
+ freed_cell->allocation.address = nullptr; |
+} |
+ |
+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; |
+} |
+ |
+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_); |
+} |
+ |
+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; |
+} |
+ |
+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 |key| 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::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; |
+ } |
+ |
+ // 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_, kNumCells + 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; |
+} |
+ |
+} // namespace trace_event |
+} // namespace base |