Answer by ewwhite for Caching/preloading files on Linux into RAM

This is also possible using the vmtouch Virtual Memory Toucher utility.

The tool allows you to control the filesystem cache on a Linux system. You can force or lock a specific file or directory in the VM cache subsystem, or use it to check to see what portions of a file/directory are contained within VM.

How much of the /bin/ directory is currently in cache?$ vmtouch /bin/           Files: 92     Directories: 1  Resident Pages: 348/1307  1M/5M  26.6%         Elapsed: 0.003426 seconds

Or...

Let's bring the rest of big-dataset.txt into memory...$ vmtouch -vt big-dataset.txtbig-dataset.txt[OOo                                                 oOOOOOOO] 6887/42116[OOOOOOOOo                                           oOOOOOOO] 10631/42116[OOOOOOOOOOOOOOo                                     oOOOOOOO] 15351/42116[OOOOOOOOOOOOOOOOOOOOOo                              oOOOOOOO] 19719/42116[OOOOOOOOOOOOOOOOOOOOOOOOOOOo                        oOOOOOOO] 24183/42116[OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOo                  oOOOOOOO] 28615/42116[OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOo              oOOOOOOO] 31415/42116[OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOo      oOOOOOOO] 36775/42116[OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOo  oOOOOOOO] 39431/42116[OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO] 42116/42116           Files: 1     Directories: 0   Touched Pages: 42116 (164M)         Elapsed: 12.107 seconds