SwapFree reported as humongous value

[mariusklocke]

On some containers lxcfs seems to report SwapFree as humongous value. Our host machines use some swap, but we also define limits.memory.swap: "false" for all our containers. So we expect 0 values for SwapCached, SwapTotal and SwapFree inside the containers. This seems to work for most containers, but with some containers we see the following:

$ lxc exec container-1 -- grep Swap /proc/meminfo
SwapCached:            0 kB
SwapTotal:             0 kB
SwapFree:       18446744073709346016 kB

Since the value is kinda close to 2^64, maybe there is some integer overflow issue involved here.

Some versions:

$ /snap/lxd/current/bin/lxcfs --version
"6.0.4"

$ lxd --version
5.21.4 LTS

Other observations:

• Occurs on Ubuntu 22.04 and 24.04 (with Linux 5.5 and 6.8)
• Not limited to a single container per machine (one machine has 4 out of 10 containers affected)