Method work

cachelib/object_cache/ObjectCacheSizeController.h:124–263

template <typename AllocatorT>
void ObjectCacheSizeController<AllocatorT>::work() {
  if (mode_ == FreeMemoryOnly) {
    auto freeMemBytes = objCache_.config_.getFreeMemBytes();
    if (freeMemBytes < objCache_.config_.lowerLimitBytes) {
      // Shrink cache when free memory is below the lower limit
      ensureFreeMemoryAboveLowerLimit();
    } else if (freeMemBytes > objCache_.config_.upperLimitBytes) {
      // Only expand cache when free memory is above the upper limit
      expandCacheByEntriesNum(objCache_.config_.expandCacheBy,
                              getCurrentEntriesLimit());
    }
    // When free memory is between lower and upper limits, do nothing (stable
    // zone)
    return;
  }

  // This function adjusts number of entries allowed in the object cache
  // based on internal metrics (average object size, total object size, max
  // entries) and system metrics (free memory and RSS).
  auto totalObjSize = getTotalObjSizeBytes();
  auto currentNumEntries = objCache_.getNumEntries();
  if (currentNumEntries == 0) {
    return;
  }
  auto minEntriesWarmCacheThreshold =
      kSizeControllerThresholdPct * objCache_.config_.l1EntriesLimit / 100;
  auto totalObjectSizeLimit = getTotalObjectSizeLimit();
  auto totalObjectSizeWarmCacheThreshold =
      kSizeControllerThresholdPct * totalObjectSizeLimit / 100;

  // Check if the cache is warming up.
  // A cache is considered to be warming up if:
  // 1. The total size of objects in the cache is less than the warm cache
  // threshold.
  // 2. The current number of entries in the cache is less than the minimum
  // entries warm cache threshold.
  // 3. There is space to grow, i.e., the current number of entries limit is
  // greater than the current number of entries.
  // If 1 and 2 are true but not 3, meaning very little items and bytes are
  // consumed, yet the cache cannot grow since (currentEntriesLimit_ ==
  // currentNumEntries), this could be because the cache shrunk to adjust for
  // large items and then the item size suddenly dropped. Without checking for
  // 3, we would not be stuck in an infinite loop where we always think the
  // cache is warming up.
  if ((totalObjSize < totalObjectSizeWarmCacheThreshold) &&
      (currentNumEntries < minEntriesWarmCacheThreshold) &&
      (currentEntriesLimit_ > currentNumEntries)) {
    // Cache is warming up.
    return;
  }

  // First thing, we want to take care of is to make sure that the total
  // object size and number of objects are within the limit.
  auto averageObjSize = totalObjSize / currentNumEntries;
  XDCHECK_NE(0u, averageObjSize);
  if (averageObjSize == 0) {
    return;
  }