Virtualization Technology News and Information
Four memory optimization techniques available in vSphere 4.1

With the release of VMware vSphere 4.1, there has been a new feature announced – memory compression.  To help explain how ESX server 4.1 manages the host memory resource, VMware has published a new whitepaper.  In it, they show experiment results that explain the performance impact for four different memory reclamation techniques: Page sharing, ballooning, memory compression and host swapping used in ESX server 4.1.  The experiment results show that:

1) Page sharing introduces negligible performance overhead.

2) Compared to host swapping, ballooning will cause much smaller performance degradation when reclaiming memory. In some cases, ballooning even brings zero performance overhead.

3) Memory compression can significantly reduce the amount of the swapped out pages and hence greatly improve the overall performance in high memory overcommitment scenario.

Here is a brief summary of the paper:

In this paper, we start from introducing the basic memory virtualization concepts. Then, we discuss the reason why supporting memory overcommitment is necessary in ESX server. Four memory reclamation techniques are currently used in ESX server: Transparent Page Sharing (TPS), Ballooning, Memory Compression and Host Swapping. We illustrate the mechanism of these techniques and analysis the Pros and Cons of each technique from performance perspective. In addition, we present how ESX memory scheduler uses a share-based allocation algorithm to allocate memory for multiple Virtual machines when host memory is overcommitted.

Beyond the technique discussion, we conduct experiments to help user understand how individual memory reclamation techniques impact the performance of various applications. In these experiments, we choose to use SPECjbb, Kernel Compile, Swingbench, SharePoint and Exchange benchmarks to evaluate different techniques.

Finally, based on the memory management concepts and performance evaluation results, we present some best practices for host and guest memory usage.

The paper can be downloaded here:

Published Monday, July 19, 2010 5:52 PM by David Marshall
There are no comments for this post.
To post a comment, you must be a registered user. Registration is free and easy! Sign up now!
<July 2010>