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Que:

1. What are the various techniques uses by ESX- server to manage the memory management and how they work?

Ans:

The ESX kernel uses transparent page sharing, ballooning and swapping to reclaim memory. Ballooning and swapping are used only when the host is running out of machine memory or a VM limit is hit.

Que:

2. What is ballooning ?

When the ESX host's machine memory is scarce or when a VM hits a Limit, The kernel needs to reclaim memory and prefers ballooning over swapping. The balloon driver is installed inside the guest OS as part of the VMware Tools installation and is also known as the vmmemctl driver.

When the ESX kernel wants to reclaim memory, it instructs the balloon driver to inflate. The balloon driver then requests memory from the guest OS. When there is enough memory available, the guest OS will return memory from its free list. When there isn't enough memory, the guest OS will have to use its own memory management techniques to decide which particular pages to reclaim and if necessary page them out to its swap- or page-file.

In the background, the ESX kernel frees up the machine memory page that corresponds to the physical machine memory page allocated to the balloon driver. When there is enough memory reclaimed, the balloon driver will deflate after some time returning physical memory pages to the guest OS again.
This process will also decrease the Host Memory Usage parameter

Ballooning is only effective it the guest has available space in its swap- or page-file, because used memory pages need to be swapped out in order to allocated the page to the balloon driver. Ballooning can lead to high guest memory swapping. This is guest OS swapping inside the VM and is not to be confused with ESX host swapping.


3. Which driver handles the ballooning

Vmmemctl driver