kmalloc

It's actually not. The pages are pages. The tail latency is avoided precisely because the page is still present and mapped, it's just been demoted to CXL instead of removed from the page tables.

So it's "zswap-ish", because reclaim migrates the page somewhere else - but in this case that somewhere else is another plain old page on another node.

If you enable zswap on top of this and give it the same size as your CXL tier, you'll end up with CXL consumed like zswap as you suggested - but the tail latencies will be higher (maybe not multi-millisecond, but i haven't tested this yet).