On 11/29/18 4:34 PM, Vojtech Pavlik wrote: > On Thu, Nov 29, 2018 at 03:35:07PM +0800, Coly Li wrote: >> On 11/29/18 11:16 AM, fangchen sun wrote: >>> hello guys, >>> >>> I want to change writeback_percent in bcache, but it seems that the >>> value is hardcoded in the bcache drive code. Why is writeback_percent >>> capped at 40 ？ Can I set it 60 or higher percent? What are risks of >>> higher percent ? >> >> I just posted a 5 patches series titled "writeback performance tuning >> options", which may permit people to set writeback percent to 70 at most >> for research purpose. >> >> Generally I don't suggest to set a higher writeback percent, a lower >> writeback percent number may start writeback thread earlier and have a >> more smooth I/O latency number. Too much dirty data on cache device may >> have negative impact for most of work load. >> >> You may try the patch set with a higher writeback percent, but unless >> you have a strong reason, I will always to use the default values firstly. > > One thing I'm wondering about: The mode (writeback/writethrough) of the > device is persistent, while the writable percentage and other tunables > need to be reset every boot (registration). It'd be very nice if all the > parameters of the bcache device were persistent. > Yes, this is one thing on my ToDo list, the rested items in the list are, - journal hang/locking issue - s390x support - 4Kn support - partition enhancement - bigger super block (this is for persistent parameters) - multiple internal B+ trees - remove multiple cache devices code framework - generate entries in /dev/disk/by-**/ directories Thanks. Coly Li
