The Memory (MB) chart displays memory data counters for virtual machines.

This chart is located in the Home view of the virtual machine Performance tab. It appears only at collection levels 2, 3, and 4.

In the descriptions below, guest physical memory refers to the virtual-hardware memory presented to a virtual machine for its guest operating system. Machine memory is actual physical RAM in the host. Note that not all counters are collected at collection level 1.

Table 1. Data Counters

Chart Label

Description

Active

Amount of guest physical memory in use by the virtual machine.

Active memory is estimated by VMkernel statistical sampling and represents the actual amount of memory the virtual machine needs. The value is based on the current workload of the virtual machine.

  • Counter: active

  • Stats Type: Absolute

  • Unit: Megabytes (MB)

  • Rollup Type: Average (Minimum/Maximum)

  • Collection Level: 2 (4)

Balloon

Amount of guest physical memory reclaimed from the virtual machine by the balloon driver.

  • Counter: vmmemctl

  • Stats Type: Absolute

  • Unit: Megabytes (MB)

  • Rollup Type: Average (Minimum/Maximum)

  • Collection Level: 1 (4)

Balloon Target

Desired amount of virtual machine balloon memory.

Balloon target memory is estimated by the VMkernel.

If the balloon target amount is greater than the balloon amount, the VMkernel inflates the balloon amount, which reclaims more virtual machine memory. If the balloon target amount is less than the balloon amount, the VMkernel deflates the balloon, which allows the virtual machine to reallocate memory when needed.

  • Counter: vmmemctltarget

  • Stats Type: Absolute

  • Unit: Megabytes (MB)

  • Rollup Type: Average (Minimum/Maximum)

  • Collection Level: 2 (4)

Consumed

Amount of guest physical memory consumed by the virtual machine for guest memory.

Consumed memory does not include overhead memory. It includes shared memory and memory that might be reserved, but not actually used.

consumed memory = memory granted - memory saved due to memory sharing

  • Counter: consumed

  • Stats Type: Absolute

  • Unit: Megabytes (MB)

  • Rollup Type: Average (Minimum/Maximum)

  • Collection Level: 1 (4)

Shared

Amount of guest physical memory available for sharing. Memory sharing occurs through transparent page sharing.

  • Counter: shared

  • Stats Type: Absolute

  • Unit: Megabytes (MB)

  • Rollup Type: Average (Minimum/Maximum)

  • Collection Level: 2 (4)

Swapped

The amount of guest physical memory swapped out to the disk by the VMkernel. This data counter measures VMkernel swapping and not to guest OS swapping.

swapped = swapout – swapin

Note:

In some cases, vMotion can skew these values and cause a virtual machine to arrive on a host with some memory already swapped out. As a result, the swapped value can be greater than the swapout – swapin value.

  • Counter: swapped

  • Stats Type: Absolute

  • Unit: Megabytes (MB)

  • Rollup Type: Average (Minimum/Maximum)

  • Collection Level: 2 (4)

Chart Analysis

A virtual machine's memory size must be slightly larger than the average guest memory usage. This enables the host to accommodate workload spikes without swapping memory among guests. Increasing the virtual machine memory size results in more overhead memory usage.

If sufficient swap space is available, a high balloon value does not cause performance problems. However, if the swapin and swapout values for the host are large, the host is probably lacking the amount of memory required to meet the demand.

If a virtual machine has high ballooning or swapping, check the amount of free physical memory on the host. A free memory value of 6% or less indicates that the host cannot meet the memory requirements. This leads to memory reclamation, which might degrade performance. If the active memory size is the same as the granted memory size, demand for memory is greater than the memory resources available. If the active memory is consistently low, the memory size might be too large.

If the host has enough free memory, check the resource shares, reservation, and limit of the virtual machines and resource pools on the host. Verify that the host settings are adequate and not lower than those set for the virtual machine.

If little free memory is available, or if you notice degradation in performance, consider taking the following actions.

Table 2. Memory Performance Enhancement Advice

#

Resolution

1

Verify that VMware Tools is installed on each virtual machine. The balloon driver is installed with VMware Tools and is critical to performance.

2

Verify that the balloon driver is enabled. The VMkernel regularly reclaims unused virtual machine memory by ballooning and swapping. Generally, this does not impact virtual machine performance.

3

Reduce the memory space on the virtual machine, and correct the cache size if it is too large. This frees up memory for other virtual machines.

4

If the memory reservation of the virtual machine is set to a value much higher than its active memory, decrease the reservation setting so that the VMkernel can reclaim the idle memory for other virtual machines on the host.

5

Migrate one or more virtual machines to a host in a DRS cluster.

6

Add physical memory to the host.