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Date: Sun, 27 Apr 2014 09:48:12 +0200
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Subject: [PROPOSAL] KSM support for KVM hosts
From: Laszlo Hornyak <laszlo.hornyak@gmail.com>
To: "dev@cloudstack.apache.org" <dev@cloudstack.apache.org>
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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

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