I came across the following parameter in kernel settings (in sysctl):
vm.min_free_kbytes
This is the amount of free memory (RAM) that's always free no matter what. In my case, I have only 1 GiB of RAM, and this parameter was set to about 64MiB. I thought that's pretty high, so I lowered it to 8MiB so far. I don't know if I can lower it any further, or if lowering it to 8MiB can cause any troubles, so the question is what would happen if the amount of the free memory was too low? Can I safely lower the value to 1MiB?