Symptoms

Consider the following scenario:

  • You have a Windows 2012 R2-based Hyper-V host cluster.

  • You create Hyper-V virtual machines on the cluster, and then you add shared virtual hard disk files (.vhdx) to the virtual machines.

In this scenario, you notice very high paged pool usage in Task Manager. If you use the Memory Pool Monitor utility (poolmon.exe), it shows that the pool tag FMfn that is allocated by fltmgr.sys uses most of the paged pool. Eventually, committed memory is exhausted. Therefore, the computer freezes. 

Cause

This issue occurs because the svhdxflt.sys driver in a particular case calls the FltGetFileNameInformation routine, and then FMfn allocation is performed. However, the svhdxflt.sys driver misses a call to the FltReleaseFileNameInformation routine to release the allocation.

Resolution

To resolve this issue, install update rollup 2975719. For more information, click the following article number to view the article in the Microsoft Knowledge Base:

2975719 August 2014 update rollup for Windows RT 8.1, Windows 8.1, and Windows Server 2012 R2

Status

Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

More Information

For more information about shared virtual hard disks, go to the following Microsoft website:

General information about shared virtual hard disksFor more information about Memory Pool Monitor, go to the following Microsoft website:

How to use Memory Pool Monitor (Poolmon.exe) to troubleshoot kernel mode memory leaksFor more information about software update terminology, click the following article number to view the article in the Microsoft Knowledge Base:

824684 Description of the standard terminology that is used to describe Microsoft software updates

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