mirror of https://github.com/facebook/rocksdb.git
94 lines
3.0 KiB
C++
94 lines
3.0 KiB
C++
// Copyright (c) 2013, Facebook, Inc. All rights reserved.
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// This source code is licensed under the BSD-style license found in the
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// LICENSE file in the root directory of this source tree. An additional grant
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// of patent rights can be found in the PATENTS file in the same directory.
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//
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// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file. See the AUTHORS file for names of contributors.
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#include "util/arena.h"
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#include <algorithm>
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namespace rocksdb {
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const size_t Arena::kMinBlockSize = 4096;
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const size_t Arena::kMaxBlockSize = 2 << 30;
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static const int kAlignUnit = sizeof(void*);
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size_t OptimizeBlockSize(size_t block_size) {
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// Make sure block_size is in optimal range
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block_size = std::max(Arena::kMinBlockSize, block_size);
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block_size = std::min(Arena::kMaxBlockSize, block_size);
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// make sure block_size is the multiple of kAlignUnit
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if (block_size % kAlignUnit != 0) {
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block_size = (1 + block_size / kAlignUnit) * kAlignUnit;
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}
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return block_size;
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}
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Arena::Arena(size_t block_size) : kBlockSize(OptimizeBlockSize(block_size)) {
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assert(kBlockSize >= kMinBlockSize && kBlockSize <= kMaxBlockSize &&
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kBlockSize % kAlignUnit == 0);
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}
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Arena::~Arena() {
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for (const auto& block : blocks_) {
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delete[] block;
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}
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}
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char* Arena::AllocateFallback(size_t bytes, bool aligned) {
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if (bytes > kBlockSize / 4) {
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++irregular_block_num;
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// Object is more than a quarter of our block size. Allocate it separately
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// to avoid wasting too much space in leftover bytes.
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return AllocateNewBlock(bytes);
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}
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// We waste the remaining space in the current block.
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auto block_head = AllocateNewBlock(kBlockSize);
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alloc_bytes_remaining_ = kBlockSize - bytes;
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if (aligned) {
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aligned_alloc_ptr_ = block_head + bytes;
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unaligned_alloc_ptr_ = block_head + kBlockSize;
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return block_head;
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} else {
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aligned_alloc_ptr_ = block_head;
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unaligned_alloc_ptr_ = block_head + kBlockSize - bytes;
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return unaligned_alloc_ptr_;
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}
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}
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char* Arena::AllocateAligned(size_t bytes) {
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assert((kAlignUnit & (kAlignUnit - 1)) ==
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0); // Pointer size should be a power of 2
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size_t current_mod =
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reinterpret_cast<uintptr_t>(aligned_alloc_ptr_) & (kAlignUnit - 1);
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size_t slop = (current_mod == 0 ? 0 : kAlignUnit - current_mod);
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size_t needed = bytes + slop;
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char* result;
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if (needed <= alloc_bytes_remaining_) {
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result = aligned_alloc_ptr_ + slop;
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aligned_alloc_ptr_ += needed;
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alloc_bytes_remaining_ -= needed;
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} else {
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// AllocateFallback always returned aligned memory
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result = AllocateFallback(bytes, true /* aligned */);
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}
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assert((reinterpret_cast<uintptr_t>(result) & (kAlignUnit - 1)) == 0);
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return result;
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}
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char* Arena::AllocateNewBlock(size_t block_bytes) {
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char* block = new char[block_bytes];
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blocks_memory_ += block_bytes;
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blocks_.push_back(block);
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return block;
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}
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} // namespace rocksdb
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