lot of MemAvailable but falling cache and raising PSI

[Stefan Priebe - Profihost AG <s.priebe@xxxxxxxxxxxx>]

Hello all,

i hope you can help me again to understand the current MemAvailable
value in the linux kernel. I'm running a 4.19.52 kernel + psi patches in
this case.

I'm seeing the following behaviour i don't understand and ask for help.

While MemAvailable shows 5G the kernel starts to drop cache from 4G down
to 1G while the apache spawns some PHP processes. After that the PSI
mem.some value rises and the kernel tries to reclaim memory but
MemAvailable stays at 5G.

Any ideas?

Thanks!

Greets,
Stefan