It might be a confusion on my part, I'm open for that possibility. The stats when using "free -h" command shows:
Mem: total 3.7G, used 301M, free 48M, shared 6.5M, buff/cache 3.4G, available 108M
Swap: total 15G, used 865M, free 14G
Since [dom0] Task Manager show my memory capacity at 96% used (in this moment of writing) it do worry me. I don't know what will happen if it reaches 100% and I do not wish to find out. And I wonder why it need to use so much buff/cache.
I'm no expert in Linux memory management, but when you have lots of buffers/cache and little of that is available, my guess is that those buffers are dirty and need to be written do disk.