Linux – Why drop caches in Linux

vmtouch seems like a good tool for the job.

Highlights:

• query how much of a directory is cached
• query how much of a file is cached (also which pages, graphical representation)
• load file into cache
• remove file from cache
• lock files in cache
• run as daemon

vmtouch manual

EDIT: Usage as asked in the question is listed in example 5 on vmtouch Hompage

Example 5

Daemonise and lock all files in a directory into physical memory:

vmtouch -dl /var/www/htdocs/critical/

EDIT2: As noted in the comments, there is now a git repository available.

Dropping the caches shouldn't take much time at all. Are you sure it's really not returning from that echo command for several hours?

It makes sense that the machine is slower after the caches are dropped, since files that it could previously read from cache now have to be read from disk.