Fedora To Further Evaluate vm.max_map_count Tuning For Better Linux Gaming Experience

There's been a Fedora 39 proposal under evaluation for boosting the kernel's vm.max_map_count to help with some Windows games on Steam Play. Though concerns were raised that bumping this kernel tunable too high may not be wise. As such, further testing is to happen for tuning Fedora's stock vm.max_map_count value.

The vm.max_map_count tunable controls the OS limits on the maximum number of memory map "mmap" areas that a process can have. Fedora uses the kernel default of 65,530 that is plenty for most software out there. But some Windows games running on Linux via Steam Play with Proton can exceed that limit. Some of the known affected games by this maximum memory map limit are Counter-Strike 2, DayZ, Hogwarts Legacy, and others.

Concerns raised by Fedora stakeholders are that jumping from 65k to 2 billion for this sysctl tunable may be too high. With a value too great, it may be possible to overload the kernel with too many mappings. In turn the Linux out-of-memory handler can terminate other processes rather than the mapping-heavy process that would lead to a bad user experience.

The 2 billion value as the proposed new maximum limit may also not be needed with some suggestions that going from 65k to a value in the 1~16 million range may be enough to satisfy some of these Windows games.

The Fedora Engineering and Steering Committee as a result has asked the change proposal owners to go ahead and try with different vm.max_map_count values rather than just going for the high maximum. We'll see what comes of this testing and how the change proposal is revised as a result.