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Reducing the amount of memory the VMkernel keeps free on ESXi 4.1 systems with at least 64GB of memory (changing minFreePct) (1033687)

Details

In ESXi 4.1 systems with at least 64GB of memory, changing the amount of memory the VMkernel keeps free in these systems can improve performance by preventing memory reclamation techniques (ballooning and swapping) from occurring too frequently.
  
The amount of memory the VMkernel keeps free is controlled by the value of minFreePct, which has a default value of 6% of managed memory. This means that when free memory is greater than or equal to 6%, the host is not under memory pressure.
 
The VMkernel uses free memory as a buffer to achieve changes to memory allocations more rapidly. Therefore, reducing minFreePct is only appropriate for systems which do not over-commit memory by more than 25%. For more information about over-committing memory, see the vSphere Resource Management Guide.

Solution

Change minFreePct to a value less than 6% and no lower than 2%. Any setting lower than 2% is not supported by VMware and is not recommended.

Note: VMware does not recommend changing the minFreePct value for systems with less than 64GB of memory.

To change the minFreePct setting for a running ESXi host:

  1. Log into the ESXi host console or use SSH. For more information, see: Using Tech Support Mode in ESXi 4.1 (1017910) and Enabling SSH on an ESXi 4.1.x host when hostd is unavailable (1033013).

  2. Set the value of minFreePct using this command:

    vsish -e set /sched/freeMemoryState/minFreePct <Percentage>

    For example, to set the value of minFreePct to 2%:

    vsish -e set /sched/freeMemoryState/minFreePct 2

    The change takes effect immediately.

To validate the current minFreePct setting on the ESXi host:

  1. Log into the ESXi host console or use SSH. For more information, see: Using Tech Support Mode in ESXi 4.1 (1017910) and Enabling SSH on an ESXi 4.1.x host when hostd is unavailable (1033013).

  2. Get the current value of minFreePct using this command:

    vsish -e get /sched/freeMemoryState/minFreePct

    Note: You can also see the change in esxtop for the minfree value, which is found in VMKMEM on the Memory screen. For more information on the esxtop command, see Performance Monitoring Utilities: resxtop and esxtop in the vSphere Resource Management Guide.

Tags

Reducing-VMkernel-memory-minFreePct

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