Recently I needed to decrease the memory reservation from one VM, but after I did that, I received the follow alert in my ESXi host:
Unable to apply DRS resource settings on host. The available memory resources in the parent pool are insufficient for the operation.
Verifying the swap file of the VM, I observed that the swap file not increased. In this case the expected behavior after decrease the memory reservation was, the increase of the swap file, but it did not happen.
When the Virtual Machine was powered off and powered on again, the alert disappeared and swap file grow up, but I needed do the same process in others VMs which I could not turn off.
After some searches on Google I found the solution in the KB2136186. This is a known issue and the fix is in the ESXi 6.0 build 3825889. In my case, my version was ESXi 6.0 U1 build 3380124, then I decided performed update in my ESXi host and after update I did some tests and the issue not occurred again. The problem was solved! 🙂