If we do underflow the know usage of a storage, recalculate it

       * actual usage (rather than relaying on cached usage), and the call to

       * this function. */

      d->usage -= removed_file_size;

    } else {

      /* If we underflowed the cached directory size, re-check the sizes of all

       * the files in the directory. This makes storage_dir_shrink() quadratic,

       * but only if a process is continually changing file sizes in the

       * storage directory (in which case, we have bigger issues).

       *

       * We can't just reset usage_known, because storage_dir_shrink() relies

       * on knowing the usage. */

      storage_dir_rescan(d);

      (void)storage_dir_get_usage(d);

    }

  }

}