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- /*
- * Copyright 2015-present Facebook, Inc.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
- #pragma once
- #include <atomic>
- #include <cassert>
- #include <cstdint>
- #include <system_error>
- #include <folly/portability/SysMman.h>
- #include <folly/portability/Unistd.h>
- namespace folly {
- namespace detail {
- class MMapAlloc {
- private:
- size_t computeSize(size_t size) {
- long pagesize = sysconf(_SC_PAGESIZE);
- size_t mmapLength = ((size - 1) & ~(pagesize - 1)) + pagesize;
- assert(size <= mmapLength && mmapLength < size + pagesize);
- assert((mmapLength % pagesize) == 0);
- return mmapLength;
- }
- public:
- void* allocate(size_t size) {
- auto len = computeSize(size);
- int extraflags = 0;
- #if defined(MAP_POPULATE)
- extraflags |= MAP_POPULATE;
- #endif
- // MAP_HUGETLB is a perf win, but requires cooperation from the
- // deployment environment (and a change to computeSize()).
- void* mem = static_cast<void*>(mmap(
- nullptr,
- len,
- PROT_READ | PROT_WRITE,
- MAP_PRIVATE | MAP_ANONYMOUS | extraflags,
- -1,
- 0));
- if (mem == reinterpret_cast<void*>(-1)) {
- throw std::system_error(errno, std::system_category());
- }
- #if !defined(MAP_POPULATE) && defined(MADV_WILLNEED)
- madvise(mem, size, MADV_WILLNEED);
- #endif
- return mem;
- }
- void deallocate(void* p, size_t size) {
- auto len = computeSize(size);
- munmap(p, len);
- }
- };
- template <typename Allocator>
- struct GivesZeroFilledMemory : public std::false_type {};
- template <>
- struct GivesZeroFilledMemory<MMapAlloc> : public std::true_type {};
- } // namespace detail
- } // namespace folly
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