| // 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/heap_profiler_allocation_register.h" |
| |
| #include "base/trace_event/trace_event_memory_overhead.h" |
| |
| namespace base { |
| namespace trace_event { |
| |
| 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::~AllocationRegister() { |
| FreeVirtualMemory(buckets_, kNumBuckets * sizeof(CellIndex)); |
| FreeVirtualMemory(cells_, num_cells_ * 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(); |
| |
| // 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; |
| } |
| |
| 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. |
| const_cast<void*&>(freed_cell->allocation.address) = nullptr; |
| } |
| |
| AllocationRegister::Allocation* AllocationRegister::Get(void* address) { |
| CellIndex* idx_ptr = Lookup(address); |
| |
| // If the index is 0, the address is not present in the table. |
| return *idx_ptr == 0 ? nullptr : &cells_[*idx_ptr].allocation; |
| } |
| |
| 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 |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::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_, 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); |
| } |
| |
| } // namespace trace_event |
| } // namespace base |