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