The filename I have suggested to put this setting to was wrong (/etc/sysctl.d/99-min-free-mem); it would be correct to name it /etc/sysctl.d/99-min-free-mem.conf (as described in /etc/sysctl.d/README: "End-users can use 60-*.conf and above").
The filename I have suggested to put this setting to was wrong (/etc/sysctl. d/99-min- free-mem) ; it would be correct to name it /etc/sysctl. d/99-min- free-mem. conf (as described in /etc/sysctl. d/README: "End-users can use 60-*.conf and above").