On Sun, Apr 27, 2014 at 3:48 AM, Laszlo Hornyak <laszlo.horn...@gmail.com> wrote: > Hi All, > > Currently Cloudstack does not manage the Linux Kernel SamePage Merger [1]. > A KSM support would allow the operator of the cloud to gain high VM > densities in the cloudstack environment by merging the redundant memory > pages. > > 1. Add new configuration setting for KSM feature > - Ignore: Instructs agent to ignore KSM setting, this allows the cloud > operator to manage KSM and good for backward compatibility > - On: Instructs agents to turn on KSM without further dealing with it > - Off: Instructs agents to turn off KSM > - Dynamic: Instructs the agent to track KSM activity periodically, turn on > or off if needed and fine-tune runtime parameters based on its performance. > > 2. Build decision logic into cloudstack agent: > - Only enable KSM if running on Linux and KSM is built into kernel > - Dynamic KSM configuration decision logic: > - Configure and tune KSM based on number of VM's, their operating > systems, the available and free processors and memory of the host. > - The configuration and status of ksm needs to be checked periodically. > > In comparison to ksmtuned, the agent logic will build on information > specific to cloud computing > - build on expectations based on the OS/template of the VM > - scale dynamically with the VM loads > - activate on VM migrations/start/stop > - respect CPU over-allocation, run ksm only when low CPU-load > > [1] https://www.kernel.org/doc/Documentation/vm/ksm.txt > > -- > > EOF
Hi Laszlo; KSM has always seemed to have a high CPU overhead when I've used it in the real world. I am curious what you think the effect will be with dynamically turning it on/off and particularly how it might impact other VM operations as well as allocation decisions. --David
