Approximate size of memory used by each entry added to the cache, including the shallow bits (sizeof) of TKey and TValue, but not the deep bits. Using 128 (bytes per chunk) / 10 (avg entries per chunk) as approximate F14 index entry size.
Declared in <folly/container/EvictingCacheMap.h>
inline constexpr static
std::size_t kApproximateEntryMemUsage = 13 + sizeof(Node);