That looks ok, ignore the cache it will be freed as soon as more ram is needed for applications. I would be more concerned about how much swap your using. 3GB is pretty low, now if you only have a basic WordPress site it should be just fine, but if you have a lot of plugins your going to have problems.
If your using large plugins you will need to adjust the PHP memory_limit to at least 512M and add to the WordPress config: define('WP_MEMORY_LIMIT', '512M');
Have to be careful though as your pretty low on ram, if the site gets busy you will not have enough. Would suggest using a WordPress cache plugin, whatever your comfortable with, I use W3-Total-Cache and have had good results with it, but needs setup to work properly.
Also would be good to adjust your swapiness, I use the value of 1 on all my machines/vm's, so it will hold off swapping as long as possible.
Swappiness is the kernel parameter that defines how much (and how often) your Linux kernel will copy RAM contents to swap. This parameters default va...
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Make sure you have at lease 2GB-4GB of swap space available, may be needed when doing updates.