When using Content Patcher mods, the game's memory usage gets out of control on Ubuntu 20.04. The most noticeable was Elle's Seasonal Buildings, memory usage increased by ~100MB each time I entered the farm map. It seems to happen with most if not all Content Patcher mods, though much slower.

I'll close this due to missing info, but there's a number of performance improvements in recent versions that might help with that.

Does that still happen if you edit the smapi-internal/config.json file in your game folder and enable the AggressiveMemoryOptimizations option? (Note that's an experimental feature and may cause crashes.)

Enabled it and seems to be no different - if it's helping, it's not by much. Got it up to ~6.1 GB of usage then stayed on the map for a bit, usage never started to decrease. It definitely feels like it's just Seasonal Buildings doing this now that I've had a bit longer to test, it was playable for hours with that one specifically disabled, odd.

As a test I installed Seasonal Buildings on Windows, and continuously warped between the farmhouse and farm; I didn't see any noticeable increase in memory usage. Does that still happen if you temporarily remove all mods except Content Patcher, Seasonal Buildings, and SMAPI itself?

Indeed, occurs with just those included. Tried with AggressiveMemoryOptimizations enabled and disabled as well.

If you keep doing it until the game runs out of available memory, does memory usage stabilize at that point or does the game crash with an OutOfMemoryException error?