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+// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
+// This source code is licensed under both the GPLv2 (found in the
+// COPYING file in the root directory) and Apache 2.0 License
+// (found in the LICENSE.Apache file in the root directory).
+//
+// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file. See the AUTHORS file for names of contributors.
+
+// Arena is an implementation of Allocator class. For a request of small size,
+// it allocates a block with pre-defined block size. For a request of big
+// size, it uses malloc to directly get the requested size.
+
+#pragma once
+#ifndef OS_WIN
+#include <sys/mman.h>
+#endif
+#include <assert.h>
+#include <stdint.h>
+#include <cerrno>
+#include <cstddef>
+#include <vector>
+#include "memory/allocator.h"
+#include "util/mutexlock.h"
+
+namespace ROCKSDB_NAMESPACE {
+
+class Arena : public Allocator {
+ public:
+ // No copying allowed
+ Arena(const Arena&) = delete;
+ void operator=(const Arena&) = delete;
+
+ static const size_t kInlineSize = 2048;
+ static const size_t kMinBlockSize;
+ static const size_t kMaxBlockSize;
+
+ // huge_page_size: if 0, don't use huge page TLB. If > 0 (should set to the
+ // supported hugepage size of the system), block allocation will try huge
+ // page TLB first. If allocation fails, will fall back to normal case.
+ explicit Arena(size_t block_size = kMinBlockSize,
+ AllocTracker* tracker = nullptr, size_t huge_page_size = 0);
+ ~Arena();
+
+ char* Allocate(size_t bytes) override;
+
+ // huge_page_size: if >0, will try to allocate from huage page TLB.
+ // The argument will be the size of the page size for huge page TLB. Bytes
+ // will be rounded up to multiple of the page size to allocate through mmap
+ // anonymous option with huge page on. The extra space allocated will be
+ // wasted. If allocation fails, will fall back to normal case. To enable it,
+ // need to reserve huge pages for it to be allocated, like:
+ // sysctl -w vm.nr_hugepages=20
+ // See linux doc Documentation/vm/hugetlbpage.txt for details.
+ // huge page allocation can fail. In this case it will fail back to
+ // normal cases. The messages will be logged to logger. So when calling with
+ // huge_page_tlb_size > 0, we highly recommend a logger is passed in.
+ // Otherwise, the error message will be printed out to stderr directly.
+ char* AllocateAligned(size_t bytes, size_t huge_page_size = 0,
+ Logger* logger = nullptr) override;
+
+ // Returns an estimate of the total memory usage of data allocated
+ // by the arena (exclude the space allocated but not yet used for future
+ // allocations).
+ size_t ApproximateMemoryUsage() const {
+ return blocks_memory_ + blocks_.capacity() * sizeof(char*) -
+ alloc_bytes_remaining_;
+ }
+
+ size_t MemoryAllocatedBytes() const { return blocks_memory_; }
+
+ size_t AllocatedAndUnused() const { return alloc_bytes_remaining_; }
+
+ // If an allocation is too big, we'll allocate an irregular block with the
+ // same size of that allocation.
+ size_t IrregularBlockNum() const { return irregular_block_num; }
+
+ size_t BlockSize() const override { return kBlockSize; }
+
+ bool IsInInlineBlock() const {
+ return blocks_.empty() && huge_blocks_.empty();
+ }
+
+ private:
+ char inline_block_[kInlineSize] __attribute__((__aligned__(alignof(max_align_t))));
+ // Number of bytes allocated in one block
+ const size_t kBlockSize;
+ // Array of new[] allocated memory blocks
+ using Blocks = std::vector<char*>;
+ Blocks blocks_;
+
+ struct MmapInfo {
+ void* addr_;
+ size_t length_;
+
+ MmapInfo(void* addr, size_t length) : addr_(addr), length_(length) {}
+ };
+ std::vector<MmapInfo> huge_blocks_;
+ size_t irregular_block_num = 0;
+
+ // Stats for current active block.
+ // For each block, we allocate aligned memory chucks from one end and
+ // allocate unaligned memory chucks from the other end. Otherwise the
+ // memory waste for alignment will be higher if we allocate both types of
+ // memory from one direction.
+ char* unaligned_alloc_ptr_ = nullptr;
+ char* aligned_alloc_ptr_ = nullptr;
+ // How many bytes left in currently active block?
+ size_t alloc_bytes_remaining_ = 0;
+
+#ifdef MAP_HUGETLB
+ size_t hugetlb_size_ = 0;
+#endif // MAP_HUGETLB
+ char* AllocateFromHugePage(size_t bytes);
+ char* AllocateFallback(size_t bytes, bool aligned);
+ char* AllocateNewBlock(size_t block_bytes);
+
+ // Bytes of memory in blocks allocated so far
+ size_t blocks_memory_ = 0;
+ AllocTracker* tracker_;
+};
+
+inline char* Arena::Allocate(size_t bytes) {
+ // The semantics of what to return are a bit messy if we allow
+ // 0-byte allocations, so we disallow them here (we don't need
+ // them for our internal use).
+ assert(bytes > 0);
+ if (bytes <= alloc_bytes_remaining_) {
+ unaligned_alloc_ptr_ -= bytes;
+ alloc_bytes_remaining_ -= bytes;
+ return unaligned_alloc_ptr_;
+ }
+ return AllocateFallback(bytes, false /* unaligned */);
+}
+
+// check and adjust the block_size so that the return value is
+// 1. in the range of [kMinBlockSize, kMaxBlockSize].
+// 2. the multiple of align unit.
+extern size_t OptimizeBlockSize(size_t block_size);
+
+} // namespace ROCKSDB_NAMESPACE