OpenVZ memory sharing

[fatzopilot]

Hi,

just a small question regarding OpenVZ and memory sharing:
If two similar identical instances are running, do they share non-kernel memory similar to KVM with KSM?
E.g. if each is running an instances of X (maybe Apache), do they share memory pages that are occupied by the X (Apache) executable?

Thanks
fatzopilot

 

[dietmar]

If two similar identical instances are running, do they share non-kernel memory similar to KVM with KSM?
E.g. if each is running an instances of X (maybe Apache), do they share memory pages that are occupied by the X (Apache) executable?

No, OpenVZ does not use KSM. Besides, memory usage is still lower in most cases.

 

[marotori]

An openvz machine will normally use less ram than you realise. This is because the machine is using space only for the program's that are running.

No ram for caching and buffers (this is done by the host)
No ram for base OS and kernel

Makes it quite lightweight!


Sent from my iPhone using Tapatalk

 

[fatzopilot]

OK, just wanted to assess whether it makes sense to invest some time in ensuring a conformant VZ setup throughout the cluster, i.e. only one webserver (nxingx) and database (postgres) and all the same version vs. a mixture (e.g. nginx, apache and postgres, mysql) in possibly different versions.
Seems like it doesn't matter and there is no such thing like KSM or shared memory and forking between the clients.

Thanks & regards,
fatzopilot

 

[hk@]

Hi
to my knowledge openvz/virtuozzo has such a feature if you start your VEs from one template and make hardlinks as new VEs; do updates only via your master-template and so on - then you can get some additional performance per hardware-node, but usually this works only if you're in control and all your VEs are built having this in mind.
regards, hk

 

[fatzopilot]

Yeah, quite interesting approach. I wonder whether pure OpenVZ is somehow thinking in the same direction. I guess in practice, this is not that relevant (maybe for some kind of shared hosting that is now done using a single Apache and VHosts or even by using Virtuozzo ) but as we all know, engineers tend to prefer the "perfect" solution....