On Wed, Nov 24, 2010 at 06:58:22PM +0800, Peter Zijlstra wrote: > On Wed, 2010-11-17 at 12:27 +0800, Wu Fengguang wrote: > > > @@ -555,8 +592,10 @@ static void balance_dirty_pages(struct a > > pause = clamp_val(pause, 1, HZ/10); > > > > pause: > > + bdi_update_write_bandwidth(bdi, &bw_time, &bw_written); > > __set_current_state(TASK_INTERRUPTIBLE); > > io_schedule_timeout(pause); > > + bdi_update_write_bandwidth(bdi, &bw_time, &bw_written); > > > > /* > > * The bdi thresh is somehow "soft" limit derived from the > > So its really a two part bandwidth calculation, the first call is: > > bdi_get_bandwidth() > > and the second call is: > > bdi_update_bandwidth() > > Would it make sense to actually implement it with two functions instead > of overloading the functionality of the one function? Thanks, it's good suggestion indeed. However after looking around, I find it hard to split it up cleanly.. To make it clear, how about this comment update? Thanks, Fengguang --- --- linux-next.orig/mm/page-writeback.c 2010-11-24 19:05:01.000000000 +0800 +++ linux-next/mm/page-writeback.c 2010-11-24 22:01:43.000000000 +0800 @@ -554,6 +554,14 @@ out: return a; } +/* + * This can be repeatedly called inside a long run loop, eg. by wb_writeback(). + * + * On first invocation it will find *bw_written=0 and take the initial snapshot. + * On follow up calls it will update the bandwidth if + * - at least 10ms data have been collected + * - the bandwidth for the time range has not been updated in parallel by others + */ void bdi_update_write_bandwidth(struct backing_dev_info *bdi, unsigned long *bw_time, s64 *bw_written) @@ -575,9 +583,12 @@ void bdi_update_write_bandwidth(struct b * When there lots of tasks throttled in balance_dirty_pages(), they * will each try to update the bandwidth for the same period, making * the bandwidth drift much faster than the desired rate (as in the - * single dirtier case). So do some rate limiting. + * single dirtier case). + * + * If someone changed bdi->write_bandwidth_update_time, he has done + * overlapped estimation with us. So start the next round of estimation. */ - if (jiffies - bdi->write_bandwidth_update_time < elapsed) + if (jiffies - bdi->write_bandwidth_update_time != elapsed) goto snapshot; written = percpu_counter_read(&bdi->bdi_stat[BDI_WRITTEN]) - *bw_written; -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>