CPU usage in centos

An old PHP backend server was checked with free-m today and found that the memory was full.

Next, press SHIFT + M, that is, sort by memory usage percentage, and find that the process ranked first occupies 0.9%. What is the occupation? Google caches some used files to the memory to improve efficiency of centos. If this is the case, I don't need such file performance, so I can release it. You can run the following two commands:

# Sync

# Echo 3>/proc/sys/Vm/drop_caches

After the memory is released, the usage is very low, as shown below: