On 9 Jul 2020, kent overstreet told this: > In real world mixed workloads LRU is fine, it's not that much of a difference > vs. the more sophisticated algorithms. More important is the stuff like > sequential_bypass or some other kind of knob to ensure your backup process > doesn't blow away the entire cache. The ioprio thing that never got integrated into bcache (but is still available as out-of-tree patches that work fine) is even better for this: yes, it might not quite be what ioprio was meant for, but it means the user has the equivalent of 'nocache' that they can apply to entire process hierarchies that they don't want to pollute the cache, just by using ionice. Run your backup with ionice -c 3 and now everything, even the metadata reads, comes from the cache if it's already in the cache but otherwise stays out of cache. (This matters if you have a huge amount of metadata that is rarely read except when the backup sweeps over it, and a not-too-huge cache device. You don't want to waste cache space on stuff that only the backup is accessing...)
