F39 proposal: Increase vm.max_map_count value (System-Wide Change proposal)

[Ben Cotton]

https://fedoraproject.org/wiki/Changes/IncreaseVmMaxMapCount

This document represents a proposed Change. As part of the Changes
process, proposals are publicly announced in order to receive
community feedback. This proposal will only be implemented if approved
by the Fedora Engineering Steering Committee.

== Summary ==
This change aims at increasing the default value of the
`vm.max_map_count` sysctl

== Owner ==
* Name: [[User:aleasto| Alessandro Astone]]
* Email: ales.astone(a)gmail.com


== Detailed Description ==
Increase the vm.max_map_count sysctl default value.

The goal is to improve compatibility with Windows games through wine
or steam. Read on "Benefit to Fedora" for examples.

Steam Deck is shipping with a default of `2147483642` (MAX_INT - 5) up
from `65530` of Fedora; it makes sense to follow their lead and set
the same value.

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This was briefly discussed in #fedora-devel and received positively.
Concerns over possible downsides were raised. I am not aware of any,
but more input here is desired.

== Benefit to Fedora ==
The following Windows games will work out of the box (through wine or steam):
* DayZ: https://steamcommunity.com/app/221100/discussions/0/3199241400256965913/
* Hogwarts Legacy: https://github.com/ValveSoftware/Proton/issues/6510
* Counter Strike 2 (Beta Windows build):
https://www.youtube.com/watch?v=i02n_Ak98TA
* Any other software that might be invoking a lot of mmaps

== Scope ==
* Proposal owners: Add the new default to `/usr/lib/sysctl.d/`

* Other developers: No work will be necessary unless the new default
is found breaking some software

* Release engineering: N/A (not needed for this Change)

* Policies and guidelines: N/A (not needed for this Change)

* Trademark approval: N/A (not needed for this Change)

* Alignment with Community Initiatives: N/A

== Upgrade/compatibility impact ==
Upgrading to the new Fedora release will seamlessly update the
default. No manual intervention is necessary.

== How To Test ==
Temporarily set the new value with `sudo sysctl -w vm.max_map_count=2147483642`

Run any of the software listed above to verify that it now works.

Or run any other software to verify the change causes no regression.


== User Experience ==
More Windows games will work out-of-the-box (through wine or steam)

== Dependencies ==
None


== Contingency Plan ==
* Contingency mechanism: Revert the shipped configuration
* Contingency deadline: Final Freeze
* Blocks release? No


== Documentation ==
The default value is currently hard-coded in the kernel, at
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/inc...
.
It cannot be changed through the kernel defconfig, instead it must be
set through sysctl.

== Release Notes ==
The default value of the vm.max_map_count sysctl is increased


-- 
Ben Cotton
He / Him / His
Fedora Program Manager
Red Hat
TZ=America/Indiana/Indianapolis