[CentOS-virt] A question about memory ballooning

Sat May 7 16:24:29 UTC 2011
carlopmart <carlopmart at gmail.com>

 >  And the opposite question, can memory balloon be deallocated?? And is
 > it possible to do this automatically or is an error to do this??

I think your understanding of ballooning may be backwards. The purpose
of the balloon driver is to give the host system a way of recovering
memory from the guest when the demands on the host's physical memory
exceed the amount available. The balloon inflates within the guests
forcing them to swap or take other memory management measures. When
the pressure on the host eases the balloon deflates automatically.


Sorry Drew, but I don't understand the use of balloon driver like you 
explains. According to RedHat's docs:

"The balloon driver allows guests to express to the hypervisor how much 
memory they require. The balloon driver allows the host to efficiently 
allocate memory to the guest and allow free memory to be allocated to 
other guests and processes.
Guests using the balloon driver can mark sections of the guest's RAM as 
not in use (balloon inflation). The hypervisor can free the memory and 
use the memory for other host processes or other guests on that host.
When the guest requires the freed memory again, the hypervisor can 
reallocate RAM to the guest (balloon deflation). "

http://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/6/html/Virtualization/para-virtdrivers.html 
(The balloon driver)

I don't see in this doc any reference to "balloon driver is to give the 
host system a way of recovering memory from the guest when the demands 
on the host's physical memory exceed the amount available"


-- 
CL Martinez
carlopmart {at} gmail {d0t} com