wb_stat
stats->nr_writeback += wb_stat(wb, WB_WRITEBACK);
stats->nr_reclaimable += wb_stat(wb, WB_RECLAIMABLE);
stats->nr_dirtied += wb_stat(wb, WB_DIRTIED);
stats->nr_written += wb_stat(wb, WB_WRITTEN);
wb->dirtied_stamp = wb_stat(wb, WB_DIRTIED);
wb->written_stamp = wb_stat(wb, WB_WRITTEN);
wb_reclaimable = wb_stat(wb, WB_RECLAIMABLE);
dtc->wb_dirty = wb_reclaimable + wb_stat(wb, WB_WRITEBACK);
dtc->wb_dirty = wb_stat(wb, WB_RECLAIMABLE);