Memory useage

[vesta_mtl]

Hi all, I'm wondering if someone can help me understand my server's memory usage.

I have a 4 GB DigitalOcean droplet running 6 WordPress websites. 20,000 total monthly pageviews.

My DigitalOcean graph shows me approaching 80% memory usage:
https://puu.sh/viAlh/1d4fdb9122.png

But free -m shows this:

Code: Select all

              total        used        free      shared  buff/cache   available
Mem:           3791        1434         131          36        2225        2017
Swap:          2047         205        1842

This doesn't match the 80% suggested by the DigitalOcean graph.

To add to the confusion, when I run htop sorted by memory I see 21 mysql processes each using 7% memory (which comes to 161% memory).
https://puu.sh/viAwd/cb1a54ef55.png

I am not sure what to make of this. Thanks in advance for any help.