Hi, I'm using bcache in Linux 5.4.45 and have been doing a number of experiments, and tuning some of the knobs in bcache. I have a very small cache device (~16 GiB) and I'm trying to make full use of it w/ bcache. I've increased the two module parameters to their maximum values: bch_cutoff_writeback=70 bch_cutoff_writeback_sync=90 This certainly helps me allow more dirty data than what the defaults are set to. But a couple other followup questions: - Any additional recommended tuning/settings for small cache devices? - Is the soft threshold for dirty writeback data 70% so there is always room for metadata on the cache device? Dangerous to try and recompile with larger maximums? - I'm still studying the code, but so far I don't see this, and wanted to confirm that: The writeback thread doesn't look at congestion on the backing device when flushing out data (and say pausing the writeback thread as needed)? For spinning media, if lots of latency sensitive reads are going directly to the backing device, and we're flushing a lot of data from cache to backing, that hurts. Thanks, Marc
