BCACHE_DEV_RATE_DW_RUNNING
if (!test_bit(BCACHE_DEV_RATE_DW_RUNNING,
set_bit(BCACHE_DEV_RATE_DW_RUNNING, &dc->disk.flags);
clear_bit(BCACHE_DEV_RATE_DW_RUNNING, &dc->disk.flags);
clear_bit(BCACHE_DEV_RATE_DW_RUNNING, &dc->disk.flags);