Re: [RFC/Feature Request] bcache: support io priority

> 2026年2月6日 10:38，yangliming <[email protected]> 写道：
> 
> Hi bcache developers,
> 
> Many business scenarios require different IO priorities. After setting IO priorities, the goal is to have high-priority writes go to the SSD cache, while low-priority requests are bypassed to the HDD. Currently, the logic is:
> ```
> 
> if ((bio->bi_opf & (REQ_RAHEAD|REQ_BACKGROUND))) {
> 
> if (!(bio->bi_opf & (REQ_META|REQ_PRIO)) &&
> 
> (dc->cache_readahead_policy != BCH_CACHE_READA_ALL))
> 
> goto skip;
> 
> } 
> ```
> 
> This logic allows IO requests to bypass, but the request type cannot be controlled in user space.
> 
> Could you support setting bypass based on IO request priority? Is such a requirement reasonable?

We had patch for caching by I/O priorities, but the interface was too complicated IMHO. For this suggestion, what is the user interface in your mind?

Thanks.

Coly Li