[pve-devel] [PATCH ksm-control-daemon 1/1] Allow to disable ksm merge_across_nodes

[Fabian Grünbichler]

On Mon, Oct 09, 2017 at 10:08:59AM +0200, Alexandre DERUMIER wrote:
> >>you can just do the same using "systemctl edit ksmtuned", and adding 
> >>just the following snippet (setting your desired value): 
> >>
> >>[Service] 
> >>ExecStartpre=... 
> >>
> >>as an extension to the existing unit. 
> 
> Yes, sure, I just want to add something easy for users. 
> (Personnaly, I think we should disable it by default, but I didn't want to break current behaviour)

personally I think we should disable KSM by default and add an explicit
opt-in that is a bigger hurdle than "apt install ksmtuned" ;)

> 
> 
> >>it would probably make more sense to just set the sysctl value 
> >>persistently though? 
> 
> AFAIK, it's not possible to setup it through sysctl, only through sysfs

yep, I misread there. still, the proper way to do this is by adding a
local systemd snippet, not by introducing a legacy environment file.

> 
> 
> >>in any case, this is IMHO not something that belongs into packaging, but 
> >>is a local configuration issue. 
> 
> I think It could be great to have something in proxmox to manage this tunning values,
> (transparent hugepage,disk readahead,...  for example too).
> Redhat have the "tuned" daemon for example to manage them for example. 
> 

IMHO this will just lead to users not knowing what they are doing
setting values and breaking their systems. the knobs are already there,
if you don't know what they are doing and how to set them, you probably
should not. I know that RH provides profiles that do automagic tuning,
but I am not sure whether those don't do more harm than good in many
cases..

maybe it would make sense to add a short chapter about KSM to the
documentation (including benefits and risks)? then we could put
the example snippt there as well..