Memory Usage - VM Test
This test reports statistics related to the usage of physical memory of the VMs.
Target of the test : A Hyper-V / Hyper-V VDI server
Agent executing the test : An internal agent
Output of the test : For a Hyper-V server, one set of results will be reported for every VM on the server
For a Hyper-V VDI server, one set of results will be reported for the user who is currently logged into each virtual desktop on the server
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Measurement | Description | Measurement Unit | Interpretation |
---|---|---|---|
Total physical memory |
Indicates the total physical memory of this VM. |
MB |
|
Used physical memory |
Indicates the used physical memory of this VM. |
MB |
|
Free physical memory |
Indicates the free physical memory of the VM. |
MB |
This measure typically indicates the amount of memory available for use by applications running on the target VM. On Unix operating systems (AIX and Linux), the operating system tends to use parts of the available memory for caching files, objects, etc. When applications require additional memory, this is released from the operating system cache. Hence, to understand the true free memory that is available to applications, the eG agent reports the sum of the free physical memory and the operating system cache memory size as the value of the Free physical memory measure while monitoring AIX and Linux guest operating systems. |
Physical memory utilized
|
Indicates the percent usage of physical memory by this VM. |
Percent |
Ideally, the value of this measure should be low. While sporadic spikes in memory usage could be caused by one/more rogue processes on the VM, a consistent increase in this value could be a cause for some serious concern, as it indicates a gradual, but steady erosion of valuable memory resources. If this unhealthy trend is not repaired soon, it could severely hamper VM performance, causing anything from a slowdown to a complete system meltdown. You can use the detailed diagnosis of this measure to figure out which processes on the VM are consuming memory excessively. |
Available physical memory |
Indicates the amount of physical memory, immediately available for allocation to a process or for system use. |
MB |
Not all of the Available physical memoryisFree physical memory. Typically,Available physical memoryismade up of theStandby List, Free List, andZeroed List. When Windows wants to trim a process' working set, the trimmed pages are moved (usually) to the Standby List. From here, they can be brought back to life in the working set with only a soft page fault (much faster than a hard fault, which would have to talk to the disk). If a page stays in the standby List for a long time, it gets freed and moved to the Free List. In the background, there is a low priority thread (actually, the only thread with priority 0) which takes pages from the Free List and zeros them out. Because of this, there is usually very little in the Free List. All new allocations always come from the Zeroed List, which is memory pages that have been overwritten with zeros. This is a standard part of the OS' cross-process security, to prevent any process ever seeing data from another. If the Zeroed List is empty, Free List memory is zeroed and used or, if that is empty too, Standby List memory is freed, zeroed, and used. It is because all three can be used with so little effort that they are all counted as "available". A high value is typically desired for this measure. This measure will be available for Windows VMs only. |
Modified memory |
Indicates the amount of memory that is allocated to the modified page list. |
MB |
This memory contains cached data and code that is not actively in use by processes, the system and the system cache. This memory needs to be written out before it will be available for allocation to a process or for system use. Cache pages on the modified list have been altered in memory. No process has specifically asked for this data to be in memory, it is merely there as a consequence of caching. Therefore it can be written to disk at any time (not to the page file, but to its original file location) and reused. However, since this involves I/O, it is not considered to be Available physical memory. This measure will be available for Windows VMs only. |
Standby memory: |
Indicates the amount of memory assigned to the standby list. |
MB |
This memory contains cached data and code that is not actively in use by processes, the system and the system cache. It is immediately available for allocation to a process or for system use. If the system runs out of available free and zero memory, memory on lower priority standby cache page lists will be repurposed before memory on higher priority standby cache page lists. Typically, Standby memory is the aggregate of Standby Cache Core Bytes,Standby Cache Normal Priority Bytes, and Standby Cache Reserve Bytes. Standby Cache Core Bytes is the amount of physical memory, that is assigned to the core standby cache page lists. Standby Cache Normal Priority Bytes is the amount of physical memory, that is assigned to the normal priority standby cache page lists. Standby Cache Reserve Bytes is the amount of physical memory, that is assigned to the reserve standby cache page lists. This measure will be available for Windows VMs only. |
Cached memory: |
This measure is an aggregate of Standby memory and Modified memory. |
MB |
This measure will be available for Windows VMs only. |
Note:
While monitoring Linux/AIX guest operating systems, you may observe discrepancies between the value of the Physical memory utilized measure and the memory usage percentages reported per process by the detailed diagnosis of the same measure. This is because, while the Physical memory utilizedmeasure takes into account the memory in the OS cache of the Linux/AIX VM, the memory usage percent that the detailed diagnosis reports per process does not consider the OS cache memory.