Method alloc

pbbslib/alloc.cc:49–78

void* mem_pool::sub_header(void* a) { return (void*)((char*)a - header_size); }

void* mem_pool::alloc(size_t s) {
  size_t log_size = log2_up((size_t)s + header_size);
  if (log_size < 20) {
    void* a = (void*)aligned_alloc(header_size, s + header_size);
    *((size_t*)a) = small_size_tag;
    return add_header(a);
  }
  size_t bucket = log_size - log_base;
  std::optional<void*> r = buckets[bucket].pop();
  size_t n = ((size_t)1) << log_size;
  used += n;
  if (r.has_value()) {
    // if (n > 10000000) std::cout << "alloc: " << add_header(*r) << ", " << n <<
    // std::endl;
    return add_header(*r);
  } else {
    void* a = (void*)aligned_alloc(header_size, n);
    // if (n > 10000000) std::cout << "alloc: " << add_header(a) << ", " << n <<
    // std::endl;
    allocated += n;
    if (a == NULL) std::cout << "alloc failed" << std::endl;
    // a hack to make sure pages are touched in parallel
    // not the right choice if you want processor local allocations
    size_t stride = (1 << 21);  // 2 Mbytes in a huge page
    auto touch_f = [&](size_t i) { ((bool*)a)[i * stride] = 0; };
    parallel_for(0, n / stride, touch_f, 1);
    *((size_t*)a) = bucket;
    return add_header(a);
  }
}

void mem_pool::afree(void* a) {
  // std::cout << "free: " << a << std::endl;