If you are curious about how Dynamic Memory (DM) is implemented in Hyper-V R2 SP1, go and take a look at Ben Armstrong’s presentation at TechEd 2010 US.

http://www.msteched.com/2010/NorthAmerica/VIR304

Expect a public beta of Windows Server 2008 R2 SP1 towards the end of July. I can tell you it is a very well architected implementation of Dynamic Memory.

Ben explains how DM works under the covers and what you can expect from SP1.

Adding memory is implemented by a Synthetic Memory Driver (VSP/VSC Pair) which requires an update of the Hyper-V Integrations in the guest partition before it can use DM.

Supported guest operating systems:

  • Windows Server 2003 (32-bit & 64bit)
  • Windows Server 2008 (32-bit & 64bit)
  • Windows Server 2008 R2
  • Widows Vista and Windows 7 (32-bit & 64-bit only)
    • Enterprise and Ultimate Editions only

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The new memory feature is clearly what it says: Dynamic Memory and NOT Memory Overcommit.

Memory Overcommit means Memory Oversubscription means Paging to the disk means Bad Performance

DM treats memory like Hyper-V treats CPU resources: as a dynamically schedulable resource.

So oversubscribing, NOT overcommitting.

New in SP1 too is the ability to protect the memory Root Reserve. By means of a registry key static memory can be set to reserve memory for the parent partition. This memory cannot be grabbed by guest partitions.

Ben also explains a new NUMA setting in the configuration of SP1 guest partitions.