text: // Copyright 2019 The TCMalloc Authors
  //
  // 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
  //
  //     https://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.
  
  #include <sys/mman.h>
  #include <unistd.h>
  
  #include <algorithm>
  #include <cstdint>
  #include <memory>
  #include <set>
  
  #include "absl/memory/memory.h"
  #include "benchmark/benchmark.h"
  #include "tcmalloc/internal/logging.h"
  #include "tcmalloc/internal/mincore.h"
  
  namespace tcmalloc {
  namespace {
  
  // Benchmark performance of mincore. We use an array on the stack to gather
  // mincore data. The larger the array the more we amortise the cost of calling
  // mincore, but the more stack space the array takes up.
  void BM_mincore(benchmark::State& state) {
    const int size = state.range(0);
  
    // If we want to place the array on the stack then the maximum frame size is
    // 16KiB. So there is no point in benchmarking sizes larger than this.
    const int kMaxArraySize = 16 * 1024;
    CHECK_CONDITION(size <= kMaxArraySize);
    auto resident = absl::make_unique<unsigned char[]>(kMaxArraySize);
  
    const size_t kPageSize = getpagesize();
    // We want to scan the same amount of memory in all cases
    const size_t regionSize = 1 * 1024 * 1024 * 1024;
    for (auto s : state) {
      uintptr_t memory = 0;
      while (memory < regionSize) {
        // Call mincore for the next section
        int length = std::min(size * kPageSize, (regionSize - memory));
        ::mincore(reinterpret_cast<void*>(memory), length, resident.get());
        memory += length * kPageSize;
      }
    }
  }
  BENCHMARK(BM_mincore)->Range(1, 16 * 1024);
  
  }  // namespace
  }  // namespace tcmalloc
  