Ah, I accidentally read over that you used free -m.

By top 3 services do you also include any programs ? For me htop itself already consumes 10 MB, what are processes are running ?

@nous@programming.dev basically hit the nail on the head looking at available and subtracting from total ram will give you the closest answer to how much ram is being used.

252 of that 592 used memory is buffers/cache, not application memory. That is used by the kernel for kernel buffers and the filesystem cache - IE files read by something at some point. The kernel keeps them in memory in case they are needed again to speed up file reads. You can effectively ignore these vales as they will always grow to fill your ram and will be evicted when programs require memory and there is not enough free.

These tools are not lieing to you, just telling you something other then what you are reading into them. Tracking and reporting on what is using memory is a complex topic and here used is just what is physically allocate. It doesn’t mean much over all as it always tends to be full of your system has been running for a decent amount of time. Available is typically the more useful one to look at as it is an estimate about how much the kernel can reclaim now if an application request it without needing to swap things out.