heim fails to report total memory usage on WSL1

[ClementTsang]

I've been having issues with using the memory library within a WSL1 instance on Ubuntu 18.04.

I tried to run the "free" example on a WSL1 instance using Ubuntu 18.04, and it fails with this error:

Error: Error { source: Kind(InvalidData), context: Some(File { path: "/proc/meminfo" }) }

It works fine on the WSL2, though.

Taking a look at the /proc/meminfo files of both of these, I think the issue is that the "MemAvailable" field doesn't exist on WSL1:

MemTotal:       33483712 kB
MemFree:        22743224 kB
Buffers:           34032 kB
Cached:           188576 kB
...

On the WSL2, it looks like:

MemTotal:       26220580 kB
MemFree:        26108576 kB
MemAvailable:   25898488 kB
Buffers:            4716 kB
Cached:             8320 kB
...

Guessing that since one field is missing, it's tripping up the number of lines check in memory.rs?

[ClementTsang]

Tested a bit more, seems like I initially messed up the comparison and the issue just seems to be on WSL1.

[svartalf]

Awesome investigation, thanks for doing it!

Based on this one function from psutil, we can't expect to have MemAvailable: line for kernels < 3.14 and should calculate it manually.