Re: What happen with vm.v_* on stable?

On 3/8/2025 12:14 PM, Rozhuk Ivan wrote:
> Hi!
>
> "vm.v_free_min", "vm.v_free_reserved", and "vm.v_free_target" sysctls describeb in i386 notes and some FBSD docs.
> I try to tune it - see no effects.
> I look into code of 14/STABLE and fail to find code that read these values.
>
> It seems it only show some initial on boot values and do nothink while OS work.
>
> Is some commits not backported from main to stable or it some refactor artefacts?
>
>
Quite a long time ago the VM system and ZFS' interaction with this 
(specifically UMA) had some very bad effects under certain workloads and 
these three sysctl's tried to mitigate that -- and not very well in some 
cases thus I wrote up a set of patches and they were under active 
discussion for some time (they solved the problem for me but not for 
everyone.)

It only bit you under certain circumstances but if it did it was pretty 
bad (e.g. 30 second no-response pauses, etc.)

I've not seen this sort of misbehavior in the last couple of major 
releases and am running fairly-heavy "same general type" workloads that 
used to be trouble with ZFS on both 13 and 14 without incident. There 
has been a LOT of improvement in these interactions in the intervening 
years and OpenZFS was brought in as well which also was involved in 
significant improvement for certain workloads.

-- 
Karl Denninger
karl@denninger.net
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