vm.min_free_kbytes setting allows kernel to compute a minimum value in the low memmory zone and reserve it for its own use.
To read the current value
[Fri Mar 24 15:18:05 root@system:~]$sysctl vm.min_free_kbytes
vm.min_free_kbytes = 1888
To set new value of 4MB. Based on your system requirement configure the value. Ideally 1.8% is good enough.
echo 4096 > /proc/sys/vm/min_free_kbytes
To configure permenantly on every reboot add the below entry to /etc/sysctl.conf