Arch: vm.max_map_count tweak superceded by config in filesystem-2024.04.07-1 or newer

[thojohns]

As of April 7, 2024, Arch Linux has set its default value for vm.max_map_count to 1048576 (source). This is higher than the previous default value of 65530 but lower than linux-tkg's default of 16777216. However, Arch's method of enforcing this value - updating /usr/lib/sysctl.d/10-arch.conf in the core filesystem package to include the line vm.max_map_count=1048576 - overrides any kernel-specific settings, unless a higher-priority config file sets it to another value.

The 'proper' solution would be to create that higher priority config file - create something like /usr/local/lib/sysctl.d/99-vm-max-map-count with the line vm.max_map_count=16777216. This is outside the scope of a kernel-only package (especially with the example /usr/local path), and probably useless for non-Arch distros, but it might be worth noting somewhere in the documentation anyways. I'm also uncertain if other distros that change the default vm_max_map_count value need similar overrides or not as I have no experience with most of them.

[ryanmusante]

Will a sysctl.conf in /etc with this entry still take precedence?

[thojohns]

Will a sysctl.conf in /etc with this entry still take precedence?

sysctl.conf isn't even read from, at least on systemd-based Arch systems, and that appears to have been the case for the last decade; I can't really test on a non-systemd setup.

The Arch wiki recommends migrating /etc/sysctl.conf to /etc/sysctl.d/99-sysctl.conf, and I can at least confirm that dropping the example conf above into /etc/sysctl.d/ also works - putting personal configs in /usr/local/ is just a personal preference of mine.