KVM KSM sharing

Submitted by masterg0g0 on Tue, 08/30/2016 - 09:50 Pro Licensee

Hello there,

I wanted to check if we have this implemented on cloudmin ?

http://www.linux-kvm.org/page/KSM
https://en.wikipedia.org/wiki/Kernel_same-page_merging

As i am coming from Proxmox, this is in there and on 16gb ram systems this saved for me 2gb ram of 2 guest KVM running with 8gb ram.
as i understand this is simply a memory saving capability for KVM running hosts..

Thanks

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Comments

Submitted by cruiskeen on Tue, 08/30/2016 - 15:54

It's an OS and kernel feature --- so you pretty much just need to turn it on in the OS. We run it on our CentOS servers.

Submitted by JamieCameron on Tue, 08/30/2016 - 23:16

Interesting ... so does this mean that VMs running the same kernel could share RAM?

It sounds cool, but on the other hand could have surprising side effects like causing RAM usage to jump if a VM upgrades its kernel.

Submitted by masterg0g0 on Wed, 08/31/2016 - 05:20 Pro Licensee

Hi Jamie,

This is something which is running on proxmox based host for quiet sometime and quiet stable.
I havent done a lot of study and am not an expert but if this could be provided as an option to activate on the KVM hosting config page or else where this could be cool. As said this is easily installable and is a Kernel feature. I am going to be installing it manually in this week on my cloudmin server.

Please give it a thought.

Submitted by cruiskeen on Wed, 08/31/2016 - 08:33

I can really only speak to CentOS and Red Hat distros but --

Strictly speaking you already have control.

On the host system :

Go into Webmin. Go to System->Bootup and shutdown.

Set ksm and ksmtuned to start at boot time (and if not running start hem).

Voila -- kernel sharing. If you feel the need to tune it, that's a little bit different matter. This may or may not be a win for you - you get less memory use at the expense of more CPU use.