RFC: system-wide default tunables

[Siddhesh Poyarekar]

On 2023-10-17 11:43, DJ Delorie wrote:
> Siddhesh Poyarekar <siddhesh@gotplt.org> writes:
>> Only stricter overrides to systemwide tunables should be allowed, e.g.
>> going from enabled memory tagging to disabled memory tagging.  For
>> numeric values such as mmap_threshold, we may need to figure out on a
>> case by case basis what constitutes "stricter".
> 
> Encoding "stricter" in the cache file might be difficult.  If we were to
> include enforcement, I'd opt for "can't override" vs "can't override
> unless stricter".
> 

That check would have to live in the code rather than in the cache file 
and would end up being per-tunable.  Maybe enhance the callback routine 
in tunable_initialize path to pass the systemwide default, allowing the 
subsystem where the tunable is initialized to decide whether the envvar 
override should stick or not.

Sid