Balloon Driver Basics?

[ranjitcool]

I have a question, always get confused with this.

1. Balloon driver is for memory only right?

2. When Host in memory stress, balloon driver inflates the memory of the vm and steals the physical memory up to 65% (default) and gives to host right?

3. When it does this, where does the host write its memory to? To a file, well that would be swapping - I get confused here, will ballooning happen to least used memory pages? It writes them to the disk and gives RAM to host?

Please guide/teach/advice

Thanks Gurus!

RJ

[J1mbo]

I wrote about balloon a while ago: http://blog.peacon.co.uk/tag/balloon/

The balloon driver is a guest level component that requests RAM from that guest, so the guest serves it from its memory pool which includes paging other areas, on the usual guest algorithm such as LRU, to disk.  But it may not need to, if sufficient RAM were available anyway (from that guests perspective).

It tends to generate less disk IO than vSwap since the guest has more knowledge of its functions than does the hypervisor..., it knows of non-pageable areas for example.

HTH

[krishnaprasad]

There is a nice guide available from VMware which talks about ballooning. http://www.vmware.com/files/pdf/techpaper/vsp_41_perf_memory_mgmt.pdf

The section "3.3 Balloonin" clearly talks about what's ballooning and how it's used.