I added this mod to an existing save and had 4-10 UPS on a semi large save file for about two to three minutes.

I understand that factorio from a modding perspective is not the best game to iterate a large amount of tiles/enities (a bit unclear on what type a resource patch is), but i would highly suggest that you decrease the number of tiles scanned per game tick.

Especially because a player without any understanding of how the mod might be implemented and that this is just a temp stall, will conclude the mod breaks the game and uninstall it.

Alternatively don't run the marking command automatically on load.

I already limit the number of chunks/entities processed per tick to what I thought was a pretty reasonable amount. Can you send me your save file so I can see if I get the same results? That number may need some tweaking or I could maybe expose it as a user-configurable option. For the record, the current settings don't affect my saves nearly that much, my UPS drops to about 40-ish while marking, and it takes less than 10 seconds to finish marking. Just as a suggestion off the top of my head, if you have a large map with a lot of unused chunks in it, DeleteEmptyChunks may help performance with a lot of things.

Save file is here - a few hours later than the point i tried to add the mod:
savefile

Neat mod - I was not aware of that one, although at the moment performance on my computer is not an issue and once load was completed everything ran smoothly

Thanks, I get the same results you did. I'm thinking it may have something to do with the very large resource patches on your map. I'll work on a fix.

Released v0.3.1 with lots of performance improvements, let me know if you still have issues.

cheers - thanks for the quick fix.