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rocksdb/port/mmap.h

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1.9 KiB

// Copyright (c) Meta Platforms, Inc. and affiliates.
// 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).
#pragma once
#ifdef OS_WIN
#include "port/win/port_win.h"
// ^^^ For proper/safe inclusion of windows.h. Must come first.
#include <memoryapi.h>
#else
#include <sys/mman.h>
#endif // OS_WIN
#include <cstdint>
#include "rocksdb/rocksdb_namespace.h"
namespace ROCKSDB_NAMESPACE {
// An RAII wrapper for mmaped memory
class MemMapping {
public:
static constexpr bool kHugePageSupported =
#if defined(MAP_HUGETLB) || defined(FILE_MAP_LARGE_PAGES)
true;
#else
false;
#endif
// Allocate memory requesting to be backed by huge pages
static MemMapping AllocateHuge(size_t length);
// Allocate memory that is only lazily mapped to resident memory and
// guaranteed to be zero-initialized. Note that some platforms like
// Linux allow memory over-commit, where only the used portion of memory
// matters, while other platforms require enough swap space (page file) to
// back the full mapping.
static MemMapping AllocateLazyZeroed(size_t length);
// No copies
MemMapping(const MemMapping&) = delete;
MemMapping& operator=(const MemMapping&) = delete;
// Move
MemMapping(MemMapping&&) noexcept;
MemMapping& operator=(MemMapping&&) noexcept;
// Releases the mapping
~MemMapping();
inline void* Get() const { return addr_; }
inline size_t Length() const { return length_; }
private:
MemMapping() {}
// The mapped memory, or nullptr on failure / not supported
void* addr_ = nullptr;
// The known usable number of bytes starting at that address
size_t length_ = 0;
#ifdef OS_WIN
HANDLE page_file_handle_ = NULL;
#endif // OS_WIN
static MemMapping AllocateAnonymous(size_t length, bool huge);
};
} // namespace ROCKSDB_NAMESPACE