keep a constant size of writeback dirty

[Stefan Priebe - Profihost AG <s.priebe@xxxxxxxxxxxx>]

Hi,

is there any way to keep a constant writeback dirty size? I have set
writeback_percent to 15 and i want bcache to keep it at 15%. Currently
it often falls below the 15% and massivly higher the i/o and latency.

I've also set congested_read_threshold_us and
congested_write_threshold_us to 0.

Greets,
Stefan