Revert of [Tracing] Add allocation register for heap profiling

base/trace_event/memory_profiler_allocation_register.h

-// 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.
-
-#ifndef BASE_TRACE_EVENT_MEMORY_PROFILER_ALLOCATION_REGISTER_H_
-#define BASE_TRACE_EVENT_MEMORY_PROFILER_ALLOCATION_REGISTER_H_
-
-#include <stdint.h>
-
-#include "base/logging.h"
-#include "base/trace_event/memory_profiler_allocation_context.h"
-
-namespace base {
-namespace trace_event {
-
-// The allocation register keeps track of all allocations that have not been
-// freed. It is a memory map-backed hash table that stores size and context
-// indexed by address. The hash table is tailored specifically for this use
-// case. The common case is that an entry is inserted and removed after a
-// while, lookup without modifying the table is not an intended use case. The
-// hash table is implemented as an array of linked lists. The size of this
-// array is fixed, but it does not limit the amount of entries that can be
-// stored.
-//
-// Replaying a recording of Chrome's allocations and frees against this hash
-// table takes about 15% of the time that it takes to replay them against
-// |std::map|.
-class BASE_EXPORT AllocationRegister {
- public:
-  // The data stored in the hash table;
-  // contains the details about an allocation.
-  struct Allocation {
-    void* address;
-    size_t size;
-    AllocationContext context;
-  };
-
-  // An iterator that iterates entries in the hash table efficiently, but in no
-  // particular order. It can do this by iterating the cells and ignoring the
-  // linked lists altogether. Instead of checking whether a cell is in the free
-  // list to see if it should be skipped, a null address is used to indicate
-  // that a cell is free.
-  class BASE_EXPORT ConstIterator {
-   public:
-    void operator++();
-    bool operator!=(const ConstIterator& other) const;
-    const Allocation& operator*() const;
-
-   private:
-    friend class AllocationRegister;
-    using CellIndex = uint32_t;
-
-    ConstIterator(const AllocationRegister& alloc_register, CellIndex index);
-
-    const AllocationRegister& register_;
-    CellIndex index_;
-  };
-
-  AllocationRegister();
-  ~AllocationRegister();
-
-  // Inserts allocation details into the table. If the address was present
-  // already, its details are updated. |address| must not be null. (This is
-  // because null is used to mark free cells, to allow efficient iteration of
-  // the hash table.)
-  void Insert(void* address, size_t size, AllocationContext context);
-
-  // Removes the address from the table if it is present. It is ok to call this
-  // with a null pointer.
-  void Remove(void* address);
-
-  ConstIterator begin() const;
-  ConstIterator end() const;
-
- private:
-  friend class AllocationRegisterTest;
-  using CellIndex = uint32_t;
-
-  // A cell can store allocation details (size and context) by address. Cells
-  // are part of a linked list via the |next| member. This list is either the
-  // list for a particular hash, or the free list. All cells are contiguous in
-  // memory in one big array. Therefore, on 64-bit systems, space can be saved
-  // by storing 32-bit indices instead of pointers as links. Index 0 is used as
-  // the list terminator.
-  struct Cell {
-    CellIndex next;
-    Allocation allocation;
-  };
-
-  // The number of buckets, 2^18, approximately 260 000, has been tuned for
-  // Chrome's typical number of outstanding allocations. (This number varies
-  // between processes. Most processes have a sustained load of ~30k unfreed
-  // allocations, but some processes have peeks around 100k-400k allocations.)
-  // Because of the size of the table, it is likely that every |buckets_|
-  // access and every |cells_| access will incur a cache miss. Microbenchmarks
-  // suggest that it is worthwile to use more memory for the table to avoid
-  // chasing down the linked list, until the size is 2^18. The number of buckets
-  // is a power of two so modular indexing can be done with bitwise and.
-  static const uint32_t kNumBuckets = 0x40000;
-  static const uint32_t kNumBucketsMask = kNumBuckets - 1;
-
-  // Reserve address space to store at most this number of entries. High
-  // capacity does not imply high memory usage due to the access pattern. The
-  // only constraint on the number of cells is that on 32-bit systems address
-  // space is scarce (i.e. reserving 2GiB of address space for the entries is
-  // not an option). A value of ~3M entries is large enough to handle spikes in
-  // the number of allocations, and modest enough to require no more than a few
-  // dozens of MiB of address space.
-  static const uint32_t kNumCells = kNumBuckets * 10;
-
-  // Returns a value in the range [0, kNumBuckets - 1] (inclusive).
-  static uint32_t Hash(void* address);
-
-  // Allocates a region of virtual address space of |min_size| rounded up to the
-  // system page size. The memory is zeroed by the system. A guard page is added
-  // after the end.
-  static void* AllocateVirtualMemory(size_t size);
-
-  // Frees a region of virtual address space allocated by a call to
-  // |AllocateVirtualMemory|.
-  static void FreeVirtualMemory(void* address, size_t allocated_size);
-
-  // Returns a pointer to the variable that contains or should contain the
-  // index of the cell that stores the entry for |address|. The pointer may
-  // point at an element of |buckets_| or at the |next| member of an element of
-  // |cells_|. If the value pointed at is 0, |address| is not in the table.
-  CellIndex* Lookup(void* address);
-
-  // Takes a cell that is not being used to store an entry (either by recycling
-  // from the free list or by taking a fresh cell) and returns its index.
-  CellIndex GetFreeCell();
-
-  // The array of cells. This array is backed by mmapped memory. Lower indices
-  // are accessed first, higher indices are only accessed when required. In
-  // this way, even if a huge amount of address space has been mmapped, only
-  // the cells that are actually used will be backed by physical memory.
-  Cell* const cells_;
-
-  // The array of indices into |cells_|. |buckets_[Hash(address)]| will contain
-  // the index of the head of the linked list for |Hash(key)|. A value of 0
-  // indicates an empty list. This array is backed by mmapped memory.
-  CellIndex* const buckets_;
-
-  // The head of the free list. This is the index of the cell. A value of 0
-  // means that the free list is empty.
-  CellIndex free_list_;
-
-  // The index of the first element of |cells_| that has not been used before.
-  // If the free list is empty and a new cell is needed, the cell at this index
-  // is used. This is the high water mark for the number of entries stored.
-  CellIndex next_unused_cell_;
-
-  DISALLOW_COPY_AND_ASSIGN(AllocationRegister);
-};
-
-}  // namespace trace_event
-}  // namespace base
-
-#endif  // BASE_TRACE_EVENT_MEMORY_PROFILER_ALLOCATION_REGISTER_H_