Finished installing truenas and started to take up 5G memory, as I continued to install other apps, the memory footprint gradually became larger, and if I continued to install apps, I was worried that truenas would stop working. Know how to set the expert, please tell me, thank you very muc
Perfectly normal; the RAM is there to be used. It’s mostly cache and will be freed if necessary.
You have a whopping 17G free! 
Expect that to go down to nearly zero in continuous operation. That’s a good thing as @dan wrote already. Free memory is wasted memory.
I am worried that this problem will cause my system to crash, it turns out that I do not know enough about the ZFS file system, just looked up the information, found that this is the working principle of the ZFS file system, thank you very much for your answer
Why would any system crash when it uses all of the memory like it should?
Yes, when I understood how the ZFS file system worked, I didn’t worry and considered adding more memory 
That remark was intended in a more general sense. I wondered what made you expect the system to crash.
Every reasonably modern system, FreeBSD, Linux, Mac OS, Windows, … will eventually use all available memory without crashing if you just leave it running continuously.
Your system will not crash.
