if a file is used a lot, does it stay in a RAM cache?

[BSD baby]

If a file is loaded off the hard drive a lot, does FreeBSD keep it in RAM?

For my high-traffic website, Apache+PHP, I have a PHP file that I'm going to be including a LOT.

The file is 3 megs, though.   Takes a few unfortunate seconds to load into memory off of disk the first time.

So - what would it take to keep it in RAM instead of being loaded off of hard drive every second of the day?

Does FreeBSD do that automatically or do I need some kind of accelerator app?

Thanks!