| // 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_HEAP_PROFILER_ALLOCATION_REGISTER_H_ |
| #define BASE_TRACE_EVENT_HEAP_PROFILER_ALLOCATION_REGISTER_H_ |
| |
| #include <stddef.h> |
| #include <stdint.h> |
| |
| #include "base/logging.h" |
| #include "base/macros.h" |
| #include "base/trace_event/heap_profiler_allocation_context.h" |
| |
| namespace base { |
| namespace trace_event { |
| |
| class TraceEventMemoryOverhead; |
| |
| // 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* const 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(); |
| explicit AllocationRegister(uint32_t num_cells); |
| |
| ~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); |
| |
| // Returns a pointer to the allocation at the address, or null if there is no |
| // allocation at that address. This can be used to change the allocation |
| // context after insertion, for example to change the type name. |
| Allocation* Get(void* address); |
| |
| ConstIterator begin() const; |
| ConstIterator end() const; |
| |
| // Estimates memory overhead including |sizeof(AllocationRegister)|. |
| void EstimateTraceMemoryOverhead(TraceEventMemoryOverhead* overhead) 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 kNumCellsPerBucket = 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 |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 maximum number of cells which can be allocated. |
| uint32_t const num_cells_; |
| |
| // 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(address)|. 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_HEAP_PROFILER_ALLOCATION_REGISTER_H_ |