[JohnFen]

Does Debian do this by default? If so, can I disable it for a performance increase?

[ac29]

No, but should you want to enable it, you can install systemd-zram-generator.

See also: https://github.com/systemd/zram-generator

As someone else mentioned, for many cases this will be a performance increase, not decrease. Compressing infrequently used memory frees up more memory to be used for filesystem caching among other things.

[stouset]

Compressed memory is a performance increase. CPUs are fast.

[JohnFen]

Depends on what sort of performance you're optimizing for, does it not?

[cmrx64]

There might be an energy hit… but there are a LOT of compute cycles available between cache fills: https://www.blosc.org/pages/blosc-in-depth/