The hypervisor removes the ballooned memory from the VM, lowering memory consumed by that VM.The balloon driver contacts the hypervisor with the details of the memory it has been allocated.That memory is now unavailable for other processes on the guest OS. The guest OS allocates memory to the balloon process.The hypervisor tells the balloon driver to request memory for a balloon process from the guest OS.The hypervisor contacts a balloon driver installed on the guest OS as part of VMware tools. ![]() TPS is enabled within VMs, however in VMware 6.0 it is disabled by default between VMs for security considerations.Ī technique in which the hypervisor reclaims idle memory from a guest OS and returns it to the host. TPS is “transparent” to the VM’s guest operating system as it does not affect the amount of memory consumed by the VM. TPS begins by breaking up large memory pages (2MB) into smaller pages (4KB), and checks the smaller pages for duplicates. VMware detects and de-duplicates identical memory pages. The following are VMware memory reclamation techniques, in order of severity: The mem.minFree value is calculated based on a sliding scale, in which 899 MB of memory is reserved for the first 28GB of physical memory, and 1% of memory is reserved for physical memory beyond 28GB. VMware initiates increasingly aggressive memory reclamation techniques as the free memory decreases further below the mem.minFree value. To gauge memory activity the hypervisor checks a random sample of the VM’s allocated memory and calculates the percent of the sample that is actively being accessed during the sampling period.įigure 2: vSphere display of a VM’s Consumed Host and Active Guest MemoryĪ Host level minimum free memory threshold that is used to trigger memory reclamation. The hypervisor does not communicate with the guest OS, so it does not know if any memory allocated to the VM is no longer needed. Hypervisor estimate of memory actively being used in the VM’s guest OS. Provisioned memory is an upper limit – when a VM is powered on, it will only consume the memory that the OS requests, and the hypervisor will continue to grant additional memory requests made by the VM until the provisioned memory limit is reached.Ĭurrent level of memory consumption for a specified VM. The amount of memory allocated to a VM plus the overhead needed to manage the VM. ![]() Total memory in use on the ESX host, which includes memory used by the Service Console, the VMKernel, vSphere services, plus the memory in use for all running VMs.įigure 1: vCenter with 37GB consumed host memory out of 64 GB physical capacity The physical memory available on the host. Today’s blog will outline basic VMware memory terms, how and when VMware memory management initiates memory reclamation, and capacity planning best practices. ![]() Our Overcommitting VMware Resources Whitepaper delivers the guidelines you need to ensure that you are properly allocating your host resources without sacrificing performance. With proper capacity planning you can estimate how much overcommitment is possible before risking performance problems. However, you can push memory overcommitment to the point where the hypervisor is unable to keep up, leading to potentially severe performance degradation on the VMs. This is possible because VMware memory management is able to recover memory that is no longer in use by the VM’s guest operating system (OS). VMware provides the ability to create virtual machines (VMs) that are provisioned with more memory than physically exists on their host servers.
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