Fedora 39 To Raise Its vm.max_map_count To Satisfy Some Steam Play Games

There's been a proposal in the works for Fedora 39 to raise its default vm.max_map_count in order to satisfy some Windows games running on Linux via Valve's Steam Play. A revised proposal has now been approved by the Fedora Engineering and Steering Committee.

Up to this point Fedora has used the default vm.max_map_count value of 65,530 while Valve's Steam OS uses a value of 2147483642 (MAX_INT - 5). Most software works just fine with the limit of the maximum number of memory maps for a process at 65k, but some Windows games like DayZ, Hogwarts Legacy, and Counter-Strike 2 need more than that for running gracefully under Steam Play.

Originally the Fedora 39 proposal was also to use a max memory map count of 2147483642, but there were concerns raised if it's too high that the kernel could be overloaded with too many mappings and in turn lead the out-of-memory handler to terminate other processes.

At this week's Fedora Engineering and Steering Committee (FESCo) meeting, they agreed to trying a value of 1,048,576 that is much higher than the current default while not as large as the SteamOS default. In any event this higher limit of vm.max_map_count should be enough to satisfy the current Windows games on Steam Play that can't get by with the lower limit.

The approval does note though that a revert will happen if any serious, practical exploits are discovered from the heightened max_map_count limit. Those wishing to easily test it themselves can do so via sudo sysctl -w vm.max_map_count=1048576.