Sorry I missed this question: > Is it the time from writeback starts to dirty reaches dirty target, or > the time from writeback starts to dirty reaches 0 ? Not quite either. I monitor the machine with zabbix; it's the time to when the backing disk reaches its background rate of activity / when writeback hits its minimum rate (writeback with the PI controller writes a little past the target because of the integral term). Viewed one way: 5/80 is just a few percent of difference (6%). But: I'm hopeful that further improvement can be made along this patch series, and in any event it's 5 minutes earlier that I/O will have an unencumbered response time after a pulse of load. Mike
