On Mon, 22 May 2017, Kuba Sztandera wrote: > I have following scenario: > - 450GiB cache device > - writeback enabled with target of 10% > > What happens is when the space taken by writeback cache is less than 45GiB > then the bcache writes one block per second every second which isn't the best. I think others have noted this as well related to a laptop. You might consider implementing a writeback_min_rate sysfs entry or something which skips writeback below some threshold. Please send us a patch if you come up with a good solution. -- Eric Wheeler > > Example: > > rate: 512/sec > dirty: 11.9G > target: 45.6G > proportional: -29.2M > derivative: 0 > change: -29.2M/sec > next io: 328ms > > This means that: > - one can hear drives clicking every second as heads snap into place > - disks never spin down even though box is fully idle > > At this rate the writeback will be flushed in about a year which is > pointless and only uses more power as disks are being kept active even > tough they don't need to. > Ssometimes it reduces sequential read performance as disks are being > wrote in random spot every second. > > Solution IMO would be either to schedule in interval longer than one > every second or let the the rate to go to 0 blocks per second when > there is not enough data in writeback cache. > Currently the writeback rate is capped to 1 block per second at minimum. > > -- > Best Regards > Jakub "Kubuxu" Sztandera > -- > To unsubscribe from this list: send the line "unsubscribe linux-bcache" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe linux-bcache" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
