Hyper-V and Dynamic Memory in Depth

Bryon SuraceSenior Program ManagerWindows Server, Hyper-VMicrosoft

VIR306

Agenda

Memory & Virtualization Memory Optimization TechniquesHyper-V Dynamic Memory

Architecture & ConceptsDemoSystem Impact

Q&A

Memory & Virtualization

Virtualization & Memory

How much memory does a server actually need?IIS Server?Print server?File server?Branch Cache?Direct Access?

How much will performance be affected if you halved the amount of memory in a VM?

Customer: Not certain how to size

“New virtual machines get 1GB of RAM [no matter what the VM is running]. I only give people more memory if they complain about performance”

“All VMs get 4GB of RAM [I have no idea what is happening with that memory] and no one complains”

“I take the minimum system requirements and add (insert one: 50%, 100%, 150%)”

“A vendor tells me their app needs 4GB of RAM. I do not have the time to test this to find out if it is true or not”

Virtualization & Memory

MemoryKey Factor to the number of running VMsThe most utilized asset in the system, but also a more expensive asset

Statistics on resource utilization of workloads CPU 10%Memory 40%Network I/O <5%Disk I/O <5%

Customer RequirementsMaximum density, without sacrificing performanceMaintain consistent performanceDon’t provide a feature that’s unsuitable for production use

Memory Management & Optimization Techniques

Ballooning

How it works:Increasing the size of the balloon forces the guest to react to memory pressure by releasing unused pagesDecreasing the size makes more memory available to the guest

VM

Memory

Host Computer

Balloon

Disk

VM

Host Computer

Memory

Balloon

DiskInflate

Swap Out

Ballloon

Deflate

VM

Host Computer

Memory

Disk

Swap In

Balloon

Deflate

Page Sharing

External Page Sharing

How it works: Eliminate redundant copies of memory pages common to more than one virtual machine

Hash all memory and store it in a table…Identify the common hashes and then…Perform a bit by bit comparison

ProblemsPage Sharing not dynamicCan take hours to share pagesThe largest benefit are zero pagesDoesn’t work with large pages

Second Level Paging

Second Level Paging

How it works: Paging at the virtualization layer by swapping VMs memory out to disk

Many problems:Swapping Guest Kernel ResourcesDouble PagingDisks are slow

But it always works…

Second Level Paging

Issue: Memory vs Disk PerformanceMemory Access:

DDR3-1600 = 5 ns; DDR3-1333 = 6 nsDDR3-1066 = 7.5 ns; DDR3-800 = 10 ns

Disk Seek Time: ~8 millisecondsFormula for comparing DDR3-800 to disk: .008/.000000010

DDR3-1600 memory is 1,600,000 times faster than diskDDR3-1333 memory is 1,333,333 times faster than diskDDR3-1066 memory is 1,066,666 times faster than diskDDR3-800 memory is 800,000 times faster than disk

Other Techniques

Guest directed page sharingMemory compressionAnd on…

Hyper-V R2 SP1Dynamic Memory Architecture & Concepts

Dynamic Memory Goals

Higher VM consolidation ratios with minimal performance impact

Dependent on:How much variation in memory utilization the workloads haveHow good a job you did of sizing the systems in the first place

Work well for both server and desktop workloadsAdd minimal overhead to the systemPass the “that looks right” test

Understanding philosophical differences

Host and Guest CollaborateUnderstands what guest information to useTrying to get the “best bang for buck” in virtual memory management

Host works in IsolationDoes not trust guest information

“black box” solution

Dynamic Memory

Benefits

Enables higher consolidation ratios per host by addressing the greatest limiting factor

to consolidation: Memory

A Production feature.

Overview

Memory is pooled and dynamically and securely distributed across VMs

Memory is dynamically added/removed based VM usage with no service interruption

Guest enlightened: guests & Hyper-V work TOGETHER

Adding/Removing Memory

Adding MemoryEnlightened fashion

Synthetic Memory Driver (VSP/VSC Pair)

No hardware emulationLight weight

Removing MemoryBallooning is more efficient

Messes up task manager in the guest OS

System Requirements

Parent Requirements:Windows Server 2008 R2 SP1Microsoft Hyper-V Server 2008 R2 SP1

Guest Requirements:Windows Server 2003, 2008 & 2008 R2

32-bit & 64-bit versions

Windows Vista and Windows 7Enterprise and Ultimate Editions only32-bit & 64-bit versions

Dynamic Memory

Adding/Removing Memory

Active Memory additionMemory is added immediately when VM needs it

Passive Memory reclamationMemory is not removed when there is no immediate needUnutilized memory is collected every 5 minutes

Startup & Max

Startup: amount of memory to boot VMBIOS does not know about DMGuest OS may not know about DMDefault: 512MB

Max: don’t let the VM above this amountDefault: 64GB

Memory Buffer & Priority

Buffer: How much “free” memory should we try and keep in the VM?

Allows for responsiveness to bursty workloadsCan be used for file cache“I like to configure my virtual machines so that they have ~20% free memory”

Priority: which VM gets the memory first1-10,000: default is 5,000The higher the priority, the higher the availability

demo

Dynamic Memory in action

Dynamic Memory APIs

Publicly Availablehttp://msdn.microsoft.com/en-us/library/cc136856(VS.85).aspxWMI interfaces come from the DMTF

Hyper-V UI Hyper-V WMI

Maximum Memory Limit

Minimum Memory Reservation

Startup Memory VirtualQuantity

Priority Weight

Dynamic Memory Buffer TargetMemoryBuffer

Dynamic memory enabled DynamicMemoryEnabled

Upgrading to R2 Service Pack 1

Any other changes to accommodate dynamic memory?

Three Steps…

Ensure Virtual Machines are ready for the updateUpdate the HostUpdate the Guest Integration Services

System Impact

Changes to Root Reserve

Hyper-V has always had the concept of a reserve of memory that is kept for the parent partition

Host Reserve - Auto-calculated based on:If the machine SLAT capabilityTotal size of host RAMNUMA architecture

Host Reserve VM Overhead Memory utilized by VMs

VM Reserve

Changes to Root Reserve

DM allows VMs to push up against the reserve consistentlyNew behavior to better protect the parent partition from rampaging virtual machines

New registry key in placeAllows you to reserve static memory for the parent partition

May result in less memory being available for VMs

What is “NUMA”?

A traditional computer:

Computer

CPU CPU CPU CPU

BUS

Memory

VM VM VM VM

VM VM VM VM

What is “NUMA”?

A NUMA computer:

Computer

CPU CPU CPU CPU

BUS

Memory

VM VM VM VM

VM VM VM VM

Back Channel

Memory

BUS

Node 1 Node 2

Why do I care?

VM memory should come from the “local NUMA node”

Computer

CPU CPU CPU CPU

BUS

Memory

VM VM VM VM

VM VM VM VM

Back Channel

Memory

BUS

Node 1 Node 2

Good!

Why do I care?

Ideally VM memory should come from the “local NUMA node”

Computer

CPU CPU CPU CPU

BUS

Memory

VM VM VM VM

VM VM VM VM

Back Channel

Memory

BUS

Node 1 Node 2

Bad

How does this work today?

Hyper-V tries to get all memory for a virtual machine from a single NUMA nodeWhen it cannot – the virtual machine “spans” NUMA nodesUsers can set preferred NUMA nodes for virtual machines in order to get the best distribution

Changes to NUMA management

Dynamic memory can result in more virtual machines spanning NUMA nodes

A virtual machine might start all on one node – but added memory might come from another node

New option to disable NUMA node spanning

Disabling NUMA Spanning

Makes the system behave like multiple small computers

Computer

CPU CPU CPU CPU

BUS

Memory

VM VM VM VM

VM VM VM VM

Back Channel

Memory

BUS

Node 1 Node 2

Download SP1 Today

Try Dynamic Memory out – for both server and desktop environments!

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