Method allocateFor

src/traffic_cache_tool/CacheTool.cc:383–454

}

Errata
VolumeAllocator::allocateFor(Span &span)
{
  Errata zret;

  /// Scaling factor for shares, effectively the accuracy.
  static const int64_t SCALE        = 1000;
  int64_t              total_shares = 0;

  if (Verbosity >= NORMAL) {
    std::cout << "Allocating " << CacheStripeBlocks(round_down(span._len)).count() << " stripe blocks from span "
              << span._path.string() << std::endl;
  }

  // Walk the volumes and get the relative allocations.
  for (auto &v : _av) {
    auto delta = v._config._alloc - v._size;
    if (delta > 0) {
      v._deficit    = (delta.count() * SCALE) / v._config._alloc.count();
      v._shares     = delta.count() * v._deficit;
      total_shares += v._shares;
    } else {
      v._shares = 0;
    }
  }
  assert(total_shares != 0);
  // Now allocate blocks.
  CacheStripeBlocks span_blocks(round_down(span._free_space));
  CacheStripeBlocks span_used{0};

  // sort by deficit so least relatively full volumes go first.
  std::sort(_av.begin(), _av.end(), [](V const &lhs, V const &rhs) { return lhs._deficit > rhs._deficit; });
  for (auto &v : _av) {
    if (v._shares) {
      CacheStripeBlocks n{(((span_blocks - span_used).count() * v._shares) + total_shares - 1) / total_shares};
      CacheStripeBlocks delta{v._config._alloc - v._size};
      // Not sure why this is needed. But a large and empty volume can dominate the shares
      // enough to get more than it actually needs if the other volume are relative small or full.
      // I need to do more math to see if the weighting can be adjusted to not have this happen.
      n             = std::min(n, delta);
      v._size      += n;
      span_used    += n;
      total_shares -= v._shares;
      Errata z      = _cache.allocStripe(&span, v._config._idx, round_up(n));
      if (Verbosity >= NORMAL) {
        std::cout << "           " << n << " to volume " << v._config._idx << std::endl;
      }
      if (!z) {
        std::cout << z;
      }
    }
  }
  if (Verbosity >= NORMAL) {
    std::cout << "     Total " << span_used << std::endl;
  }
  if (OPEN_RW_FLAG) {
    if (Verbosity >= NORMAL) {
      std::cout << " Updating Header ... ";