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

[phoronix]

Phoronix: 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...

https://www.phoronix.com/news/Fedora-39-Max-Map-Count-Approve

[Sethox]

The statement

they agreed to trying a value

doesn't give much credence for the need of the change. It sounds like the next Fedora version are going to beta testers.
In my personal opinion, make it easier to change the limit and/or let users know when gaming change the limit and have advisable tips on set numbers since too high will "break" other workflow (make it a note of it for the users to understand) instead of forcing the change on every user.

[peppercats]

The statement doesn't give much credence for the need of the change. It sounds like the next Fedora version are going to beta testers.
In my personal opinion, make it easier to change the limit and/or let users know when gaming change the limit and have advisable tips on set numbers since too high will "break" other workflow (make it a note of it for the users to understand) instead of forcing the change on every user.

They're using the same value Steam sets the default at on Steam Deck.
There's really no downside to this, as programs that would use more memory under it simply wouldn't work without it.

https://www.suse.com/support/kb/doc/?id=000016692

1. Are there any side effects due to significantly increasing the vm.max_map_count?

Increasing this parameter will potentially increase memory consumption by an application and thereby reduce performance of the server. However, this is entirely dependent upon an application allocating a large amount of memory maps.

2. Is there an absolute maximum number that can be specified for vm.max_map_count?

Theoretically, yes -- MAXINT for the architecture. But the server will run out of memory long before an application hits these limits.

3. How does increasing vm.max_map_count impact the kernel memory footprint?

Each mapped area needs some kernel memory. At least a vm_area_struct must be allocated, i.e. around 128 bytes per map count (plus some small overhead added by the SLAB allocator if additional slabs are needed). When vm.max_map_count is larger, processes are allowed to make the kernel allocate more memory for this purpose.

4. Does the kernel preallocate memory according to this setting?

No. The memory is allocated only when a process actually needs the map areas.

5. Does increasing this limit have any performance impact (e.g. more CPU time to scan memory map)?

No. The increase of this limit does not by itself change anything. Only processes which actually use a large amount of memory maps are affected.

[erniv2]

Ahh reminds me of the good old windows xp teaks.

SystemPages=0xffffffff

[sophisticles]

Another option is to play Windows games on, oh I don't know, Windows, maybe?

Yes, I know some games will play fine under Linux with WINE, but many don't and if you are into Windows games either buy an XBOX or run a dual boot like i do.

[discordian]

What the heck are those games doing to end up with 65k memory mappings?
besides, if someone would ask me where to change it, I would've guessed this being handled by ulimit.

[theriddick]

Star Citizen and some mods like RogueTech certainly would hit this issue as they do a lot of things in the background.
Another issue that nobody thinks about is swap file limits, or lack of.

Lots of my games will eat a certain high value swap size and if it can't get it, they cause the system to break. I run a 40gb swap file because Linux doesn't do dynamic swap.

[pieman]

Another option is to play Windows games on, oh I don't know, Windows, maybe?

Yes, I know some games will play fine under Linux with WINE, but many don't and if you are into Windows games either buy an XBOX or run a dual boot like i do.

NO. You can play with Windows, but I'm sticking to Linux and gaming on it instead. If the game doesn't work, there are other games. I'm done with toying with Windows. I like Linux. I prefer Linux, I am going to game on Linux. I'd rather spend the time with wine and proton, than deal with Windows.

[aviallon]

Star Citizen and some mods like RogueTech certainly would hit this issue as they do a lot of things in the background.
Another issue that nobody thinks about is swap file limits, or lack of.

Lots of my games will eat a certain high value swap size and if it can't get it, they cause the system to break. I run a 40gb swap file because Linux doesn't do dynamic swap.

Actually, you can have dynamic swap, by automatically creating and adding new swap files as needed.
There are already a few tools for that. In the past, I used systemd-swap, but that is deprecated and unmaintained.

[theriddick]

Actually, you can have dynamic swap, by automatically creating and adding new swap files as needed.
There are already a few tools for that. In the past, I used systemd-swap, but that is deprecated and unmaintained.

Yeah their all old and complicated things to setup. I looked at a few but couldn't understand the language.