Thats not really an issue. Buffered RAM on the Guest is used RAM on the Linux host. So it works as intended.
Maybe we should start an feature request to add more infos to the ram usage graph.
I for example would like something like this...
...instead of that:
There are 3 annoying cases where you can't trust the default graphs:
1.) If you use ballooning with different min/max RAM values. My VM for example got 8GB max and 4GB min RAM. From 11th to 12th dec the used RAM is stagnating at 4G and you think another 4GB are free and can be used but because ballooning kicked in the useable RAM was limited to 4GB. So at that time the VM used 4GB of 4GB and not 4GB of 8GB what the default graph is telling you. So you think half of the RAM is free but in reality it nearly 100% used.
Because of that I would like something like my red "N/A" graph what will tell you how much of the RAM is "blocked" by ballooning and not available anymore for the guest.
2.) The second thing is that you can't see how much of the used RAM is used for buffering/caching. Everyone is confused because of that. From the hosts point of view you want to see the total amount of RAM used by the guest, like the default graph is showing it for Linux VMs.
From the guests point of view you don't care how much RAM is used in total, because most OSs will grab as much RAM as possible for buffering/caching and the total RAM usage is always above 90%, whatever RAM size you choose. Here it would be great to see how much of the used RAM is used for unimportant stuff like caching/buffering what could be freed easily if a service needs more RAM.
So I think it would be nice to differentiate the used RAM like in my edited graph where light blue is the total RAM including buffer/cache (like default) but there is also a dark blue graph which only shows RAM actively used by the system and user processes. So its basically the used RAM without cache/buffer, so you can see early if a guest gets short on memory to increase it. If a OS only gives information on one of the two things, then just show that one thing. But in that case you atleast know if it is with or without buffering/caching.
3.) Not all guest OSs are handled the same...
For Linux "used" is everything incl. buffered/cached RAM.
For Win10 "used" is only RAM used by the system and programs. RAM used for Caching isn't take into account.
For Unix (atleast my FreeBSD/OPNsense) there is no way to get usefull information. The virtio ballooning implementation of FreeBSD isn't reporting RAM stats so Proxmox falls back to the kvm process that VM is using. So "used" RAM is the amount of reserved RAM by that process. The problem is that this process reserves as much RAM as possible. If you give that VM 12GB RAM, KVM will reserve and block 11.6GB of that RAM, even if the guest is only using 400MB of RAM including buffering and caching. So 11.2GB of RAM are totally wasted and not usable by other VMs or the guest.
