I came across an interesting problem where hypervisor's memory was ballooning although there wasn't a memory contention on the host.
Problem:
Host has 32GB of RAM and provisioned RAM is 20GB, there was absolutely no reason for Memory swapping or Ballooning but when I did SSH and esxtop then 'm' for memory, you can see in the screenshot memory swapping is taking place:
This was confirmed from the VIClient Performance tab as well where 1.5GB of hypervisor's memory was in used by Baloon drivers.
I've also added screenshot from VKernel vOPS
After going back to basis and checking esxtop again, I found that although MEMSZ is 2048MB the GRANT memory is 449.11MB this tells me something is wrong with resource allocation.
On checking VM Properties, strangely there is a limit of 512MB on the memory resources which is not visible in Summary and you can also see from the screenshot memory limit bar wasn't moved or adjusted to 512MB.
You can also run following command (change the VMNAME) to identify the memory size and maximum memory size
egrep "memsize|sched.mem.max" /vmfs/volumes/*/*/VMNAME.vmx | awk -F/ '{print $6}' | more
Solution:
After completing the VMotion check the performace monitor and see memory release from the Balloon drivers and difference in VM performance and VM memory chart.
Possible Cause:
Problem:
Host has 32GB of RAM and provisioned RAM is 20GB, there was absolutely no reason for Memory swapping or Ballooning but when I did SSH and esxtop then 'm' for memory, you can see in the screenshot memory swapping is taking place:
This was confirmed from the VIClient Performance tab as well where 1.5GB of hypervisor's memory was in used by Baloon drivers.
I've also added screenshot from VKernel vOPS
After going back to basis and checking esxtop again, I found that although MEMSZ is 2048MB the GRANT memory is 449.11MB this tells me something is wrong with resource allocation.
On checking VM Properties, strangely there is a limit of 512MB on the memory resources which is not visible in Summary and you can also see from the screenshot memory limit bar wasn't moved or adjusted to 512MB.
You can also run following command (change the VMNAME) to identify the memory size and maximum memory size
egrep "memsize|sched.mem.max" /vmfs/volumes/*/*/VMNAME.vmx | awk -F/ '{print $6}' | more
Solution:
If
sched.mem.max is smaller than memsize, the balloon driver can start consuming memory
(especially if the guest operating system application has periodic bursts of
memory usage). However, this setting can cause the balloon driver to retain its
hold on memory. If the guest operating system requires memory that is made
unavailable by the balloon driver, the guest operating system starts using swap
memory instead, which slows it down considerably.
To force the balloon driver to release its hold on
memory and prevent the guest operating system from using swap space, use one of
these options:
- Set the value of sched.mem.max to the allocated memory or greater.
- Select the virtual machine's Resources > Memory > Limit > Unlimited box.
- Migrate the virtual machine to another host.
After completing the VMotion check the performace monitor and see memory release from the Balloon drivers and difference in VM performance and VM memory chart.
Possible Cause:
Migrating a virtual machine from ESX 2.x to 3.x
or 4.x may cause a carry-over of memory reservation that is smaller than the
virtual machine's allocated memory (likely a customer-specific
setting).
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