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Measures reported by XenMemMemoryTest
When computing the memory footprint of a Xen host, there are two components that must be taken into consideration. First, there is the memory consumed by the Xen hypervisor itself. The hypervisor is a software program that manages multiple operating systems (or multiple instances of the same operating system) on a single computer system. It manages the system's processor, memory, and other resources to allocate what each operating system requires. Hypervisors are designed for a particular processor architecture and may also be called virtualization managers.
The other component that can impact the memory consumption of a XenServer host is the control domain. The control domain is a privileged VM that provides low-level services to other VMs, such as providing access to physical devices. It also runs the management tool stack.
The XenMemMemoryTest reports the memory usage of the control domain and hypervisor of the XenServer, and enables administrators to judge whether/not adequate free memory is available on the XenServer host for use by the virtual machines.
| Measurement |
Description |
Measurement
Unit |
Interpretation |
| Free_memory |
Indicates the amount of free memory available at the host |
MB |
Ideally, the value of this measure should be very high. If the value of this measure is very low or is steadily decreasing, it is indicative of a severe memory erosion at the host. By viewing the values reported by this measure along with the Memory_usage metric, administrators can easily figure out where memory-intensive processes are executing - at the control domain level or at the hypervisor level?
To view the processes responsible for the low free memory at the control domain-level, click on the DIAGNOSIS icon (the magnifying glass icon) against the control_domain descriptor in this page. The resulting Detailed Diagnosis page lists the top-10 memory-consuming processes execuitng on the control domain. Note that this capability is available for the control_domain descriptor only. You might want to kill one/more processes to restore memory usage to normalcy.
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| Total_memory |
Indicates the total physical memory available for use at the host |
MB |
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| Memory_usage |
Indicates the percentage of memory used |
Percent |
Ideally, this value should be low. A high value of this measure for the control_domain or the xen_server (i.e., the hypervisor) descriptor, indicates that the control domain or the hypervisor is consuming memory excessively. Viewing the value reported by this measure alongside that of Free_memory will accurately point administrators to the root-cause of the problem - is it the control domain or the hypervisor? Memory contention at the host can hamper the memory availability of the guests, thereby adversely impacting guest performance. By allocating more physical memory to the host, administrators can ensure that processes executing on the host do not contend for limited memory resources.
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