[SOLVED] High memory buff/cache on pve node

[rian81]

Hi,

I have got some issue on pve node memory:

1. when check at the console
root@CBN-node2:~# free -h
total used free shared buff/cache available
Mem: 251Gi 23Gi 176Gi 66Mi 53Gi 228Gi
Swap: 8.0Gi 10Mi 8.0Gi

2. when check on dashboard, only 23Gi

why is there a difference? why is the memory buff/cache high?

Thanks,

Here my pve version

# pveversion --verbose
proxmox-ve: 8.1.0 (running kernel: 6.2.16-3-pve)
pve-manager: 8.1.4 (running version: 8.1.4/ec5affc9e41f1d79)
proxmox-kernel-helper: 8.1.0
pve-kernel-6.2: 8.0.5
proxmox-kernel-6.5: 6.5.11-7
proxmox-kernel-6.5.11-7-pve-signed: 6.5.11-7
proxmox-kernel-6.2.16-20-pve: 6.2.16-20
proxmox-kernel-6.2: 6.2.16-20
pve-kernel-6.2.16-3-pve: 6.2.16-3
ceph: 17.2.7-pve1
ceph-fuse: 17.2.7-pve1
corosync: 3.1.7-pve3
criu: 3.17.1-2
glusterfs-client: 10.3-5
ifupdown2: 3.2.0-1+pmx8
ksm-control-daemon: 1.4-1
libjs-extjs: 7.0.0-4
libknet1: 1.28-pve1
libproxmox-acme-perl: 1.5.0
libproxmox-backup-qemu0: 1.4.1
libproxmox-rs-perl: 0.3.3
libpve-access-control: 8.0.7
libpve-apiclient-perl: 3.3.1
libpve-common-perl: 8.1.0
libpve-guest-common-perl: 5.0.6
libpve-http-server-perl: 5.0.5
libpve-network-perl: 0.9.5
libpve-rs-perl: 0.8.8
libpve-storage-perl: 8.0.5
libspice-server1: 0.15.1-1
lvm2: 2.03.16-2
lxc-pve: 5.0.2-4
lxcfs: 5.0.3-pve4
novnc-pve: 1.4.0-3
proxmox-backup-client: 3.1.2-1
proxmox-backup-file-restore: 3.1.2-1
proxmox-kernel-helper: 8.1.0
proxmox-mail-forward: 0.2.2
proxmox-mini-journalreader: 1.4.0
proxmox-widget-toolkit: 4.1.3
pve-cluster: 8.0.5
pve-container: 5.0.8
pve-docs: 8.1.3
pve-edk2-firmware: 4.2023.08-2
pve-firewall: 5.0.3
pve-firmware: 3.9-1
pve-ha-manager: 4.0.3
pve-i18n: 3.1.5
pve-qemu-kvm: 8.1.2-6
pve-xtermjs: 5.3.0-3
qemu-server: 8.0.10
smartmontools: 7.3-pve1
spiceterm: 3.3.0
swtpm: 0.8.0+pve1
vncterm: 1.8.0
zfsutils-linux: 2.2.2-pve1

 

[Dunuin]

Please read https://linuxatemyram.com to get a better understanding whats the difference between "free" and "available" RAM.

Free RAM is wasted performance/money so every OS will use all free RAM for caching if not needed for other purposes. RAM used for caching is then actually in use but the OS can easily free it up once needed, so RAM used for caching counts at the same time as "available".
So while you only got 23GiB of "free" RAM (which free -h as well as PVE are reporting) there is (according to free -h) still 228GiB of RAM "available" that could be used.

 

[rian81]

Yes, i know about free and available RAM, my question is why buff/cache memory on pve node high, because it trigger our monitoring and a few days ago buff/cache reached 160Gi, and i did clear buff/cache manually

 

[Dunuin]

Like said, normal behaviour of any OS including Linux. If there is any disk IO it will be cached in RAM if there is lots of RAM not used for anything else. So the problem is your monitoring and not that PVE is caching stuff
Or do you prefer a slow hypervisor just so your monitoring software will stop complaining?^^
Would be better to fix the triggers of your monitoring software to only alert you in case "available" RAM gets low instead of running out of "free" RAM. So you are monitoring the wrong metrics.

 

[rian81]

Noted, thanks

 

[rian81]

Hi,

For this case only happened on cluster PVE8, my other cluster that use PVE7, memory buff/cache only around 5-8G

Thanks