code: private void adjustCacheSizes() {
          long newSharedCacheSize = voldemortConfig.getBdbCacheSize() - this.reservedCacheSize;
          logger.info("Setting the shared cache size to " + newSharedCacheSize);
          for(Environment environment: unreservedStores) {
              EnvironmentMutableConfig mConfig = environment.getMutableConfig();
              mConfig.setCacheSize(newSharedCacheSize);
              environment.setMutableConfig(mConfig);
          }
      }
docs: When a reservation is made, we need to shrink the shared cache
  accordingly to guarantee memory foot print of the new store. NOTE: This
  is not an instantaneous operation. Changes will take effect only when
  traffic is thrown and eviction happens.( Won't happen until Network ports
  are opened anyway which is rightfully done after storage service).When
  changing this dynamically, we might want to block until the shared cache
  shrinks enough