Performance By Design

This is a continuation of a series of blog posts on VMware memory management. The previous post in the series is here . In this installment, I will discuss the impact and effectiveness of transparent memory sharing, using the performance data that was gathered during a benchmark that stressed VMware's virtual memory management capabilities. Transparent memory sharing. Transparent memory sharing is one of the key memory management mechanisms that supports aggressive server consolidation. Dynamically, VMware detects memory pages that are identical within or across guest machine images. When identical pages are detected, VMware maps them to a single page in machine memory. When guest machines are largely idle, transparent memory sharing enables VM to pack guest machine images efficiently into a single hardware platform, especially for machines running the same OS, the same OS version, and the same applications. However, when guest machines are active, the benefits of transparent m...

This is a continuation of a series of blog posts on VMware memory management. The previous post in the series is here . Case Study. The case study reported here is based on a benchmark using a simulated workload that generates contention for machine memory. VMware ESX Server software was installed on a Dell Optiplex 990 with an Intel i7 quad-core processor and 16GB of RAM. (Hyper-Threading was disabled on the processor through the BIOS.) Then four identical Windows Server 2012 guest machines were configured, each configured to run with 8 GB of physical memory. Each Windows guest is running a 64-bit application benchmark program designated as the ThreadContentionGenerator.exe, which the author developed. The benchmark program was written using the .NET Framework. The program allocates a very large block of private memory and accesses that memory randomly. The benchmark program is multi-threaded, and updates the allocated array using explicit locking to maintain the integrity of its ...

Server virtualization technology, as practiced by products such as the VMware ESX hypervisor, applies similar virtual memory management techniques in order to operate an environment where multiple virtual guest machines are provided separate address spaces so they can execute concurrently, sharing a single hardware platform. To avoid confusion, in this section machine memory will refer to the actual physical memory (or RAM) installed on the underlying VMware Host platform. Virtual memory will continue to refer to virtual address space a guest OS builds for a process address space. Physical memory will refer to a virtualized view of machine memory that VMware grants to each guest machine. Virtualization adds a second level of memory address virtualization. (A white paper published by VMware entitled "“ Understanding Memory Resource Management in VMware® ESX™ Server ” is a good reference.) When VMware spins up a new virtual guest machine, it grants that machine a set of contiguous v...

Virtual memory management refers to techniques that operating systems employ to manage the allocation of physical memory resources (or RAM) on demand, transparent to the applications that execute on the machine. Modern operating systems, including IBM’s proprietary mainframe OSes, virtually all flavors of Unix and Linux, as well as Microsoft Windows, have uniformly adopted virtual memory management techniques, ever since the first tentative results from using on-demand virtual memory management demonstrated more effective utilization of RAM, compared to static memory partitioning schemes. All but the simplest processor hardware offer support for virtual memory management. VMware is a hypervisor , responsible for running one or more virtual machine guests, providing each guest machine with a virtualized set of CPU, memory, disk and network resources that VMware is then responsible for allocating and managing. With regard to managing physical memory, VMware initially grants each vir...

This is the beginning a new series of blog posts that explores the strategies that VMware ESX employs to manage machine memory, focusing on the ones that are designed to support aggressive consolidation of virtual machine guests on server hardware. Server consolidation is one of the prime cost justifications for the use of VMware’s virtualization technology. Typical rack-mounted blade servers that are deployed in data centers contain far more processing power than most application servers require. From a capacity planning perspective, it is simply not cost-effective to configure many server images today to run directly on native hardware. Virtualization software permits server resources – CPUs, memory, disk and network – to be carved up into functional sub-units and then shared among multiple tenants, known as guest machines. Aggregating multiple server images onto blade servers using virtualization provides compelling operational benefits, including rapid recovery from failures ...