serverfault - Caching/preloading files on Linux into RAM
StackExchange - Unix & Linux -Can I configure my Linux system for more aggressive file system caching?

Hoytech - vmtouch - the Virtual Memory Toucher, GitHub - hoytech/vmtouch. See Freshports - sysutils/vmtouch for a FreeBSD version.
GitHub - Feh/nocache minimize caching effects
GitHub - tobert/pcstat Page Cache stat: get page cache stats for files on Linux
GitHub - datenwolf/fmlock map files into memory and lock them there