wait_for_writeback
int wait_for_writeback = 0;
wait_for_writeback = 1;
if (wait_for_writeback)
zswpwb_after = wait_for_writeback(cgroup, 5000);
if (wait_for_writeback(wb_group, 5000) > 0 && get_cg_wb_count(zw_group) == 0)