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Windows server 2008 R2 Standard and Windows server 2008 Standard differences in cached memories reported by WMI and task manager RRS feed

  • Question

  • Hello,

    A Brief Background:

    I am trying to fetch the system cached memory details of Windows Server 2008 Standard and Windows Server 2008 R2 Standard .

    I am querying Win32_PerfFormattedData_PerfOS_Memory class of WMI to get values of following fields :-

    CacheBytes, StandbyCacheReserveBytes, StandbyCacheNormalPriorityBytes, ModifiedPageListBytes, StandbyCacheCoreBytes.

    The system cached memory is addition of above 5 fields according to the documentation of MSDN. Here is the link

    http://msdn.microsoft.com/en-us/library/aa965225%28VS.85%29.aspx#system_memory_performance_information

    For verification of the System Cached memory values I am viewing task manager's Physical Memory section under Performance tab.

    Problem:-

    Observation for Windows Server 2008 Standard

    Now, when I do a WMI query and add the values returned for above mentioned 5 fields, I can see the System Cached memory shown in task manager exactly equal to addition of these 5 fields. Which is in accordance to what the documentation says.

    On the other hand, for Windows Server 2008 R2 Standard

    When I fetch the values of CacheBytes, StandbyCacheReserveBytes, StandbyCacheNormalPriorityBytes, ModifiedPageListBytes, StandbyCacheCoreBytes from WMI class Win32_PerfFormattedData_PerfOS_Memory.

    The value for System Cached memory exceeds exactly by the value equal to "CacheBytes".

    Evidently, it is observed repeatedly for across all the R2 systems, I can get the System cached memory by doing an addition of only StandbyCacheReserveBytes, StandbyCacheNormalPriorityBytes, ModifiedPageListBytes, StandbyCacheCoreBytes. That means here if we add CacheBytes field we would get incorrect System Cached memory. This certainly proves that my observations are not in sync with the above documentation mentioned.

    I wish to ask if is this the way it should work , or if there is anything which is documented about why Cached Memory shows variation from expected behavior for R2 systems when calculated from WMI class's 5 fields?

    Please let me know if you need any more information to answer this question.

    Thanks in advance. 
    Monday, January 6, 2014 5:41 AM