if err := out.Mmap(total); err != nil { // Mmap will copy out.heap over to out.buf
			Exitf("mapping output file failed: %v", err)
		}
	}
	return true
}

// maxOutBufHeapLen limits the growth of the heap area.
const maxOutBufHeapLen = 10 << 20

// writeLoc determines the write location if a buffer is mmaped.
// We maintain two write buffers, an mmapped section, and a heap section for