TCMalloc cache size is 1.5 MB. We should experiment with a larger size for the per cpu caches. This logic needs to set the cache size at CpuCache::Activate() time. The behavior will be controlled by a environment variable
MONGO_TCMALLOC_MAX_TOTAL_THREAD_CACHE_BYTES
We should use similar logic to the gperftools tcmalloc. 

This behavior cannot be controlled by server parameter since the cpu cache size is determined as part of a C++ static initializer.