eG Help

If one/more VMs on a Hyper-V host are over-sized with physical memory resources, it can result in a serious memory contention that may not only affect the host, but also other VMs on the host. By tracking the physical memory allocation to the VMs on a Hyper-V host, administrators can proactively detect over-allocations and can initiate remedial actions before the problem impacts performance. For this, administrators can use the HvOSMemoryTest test.

This test monitors the physical memory allocated to the VMs, and points to those VMs that are allocated more resources than required.

Measurement	Description	Measurement Unit	Interpretation
Total_phy_mem	Indicates the total physical memory capacity of the host.	MB
Used_phy_mem	Indicates amount of physical memory allocated to VMs.	MB
Physical_mem_utilze	Indicates the percentage of physical memory that is allocated to the VMs on the host.	Percent	Ideally, this value should be low. A value close to 100% is indicative of over-allocation of physical memory to the VMs. You can use the detailed diagnosis of this measure to identify which VM has been allocated maximum resources.
Free_phy_mem	Indicates the amount of physical memory unusued on the host.	MB	Ideally, the value of this measure should be high. A low value or a consistent decrease in this value is a cause for concern, as it indicates excessive memory usage by the VMs on the host.
Available_phy_mem	Indicates the amount of physical memory, immediately available for allocation to a process or for system use.	MB	Not all of the Available_phy_mem is Free_phy_mem. Typically, Available_phy_mem is made up of the Standby List, Free List, and Zeroed 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.
Modified_mem	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_phy_mem.
Standby_mem	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_mem 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.
Cached_mem	This measure is an aggregate of Standby_mem and Modified_mem.	MB