get_cg_wb_count
count = get_cg_wb_count(cg);
zswpwb_before = get_cg_wb_count(cgroup);
zswpwb_after = get_cg_wb_count(cgroup);
if (wait_for_writeback(wb_group, 5000) > 0 && get_cg_wb_count(zw_group) == 0)