I haven't used swap on zvol myself, but I've read about issues in low-memory situations, like this one: https://github.com/openzfs/zfs/issues/7734
To write to swap, zfs needs to allocate ARC memory. But to do that, it would need to write to swap...
Consider using zramswap, that's probably the easiest solution.
You shouldn't use swap on zvol in Linux at all. It will lead to dead lock when high memory pressure. See also https://github.com/openzfs/zfs/issues/7734
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