Looking through old bug tickets... I think you should rather use hotpluggable memory here for the guests instead - or use a big swap partition on the host. Anyway, this is not a bug, so closing this ticket now.
** Changed in: qemu Status: New => Invalid -- You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. https://bugs.launchpad.net/bugs/1192065 Title: qemu release memory to system Status in QEMU: Invalid Bug description: Qemu pre-allocates the maximum balloon amount which is inconvinient if all of the memory is used up and some other system needs to be added memory resource eg:- I have 4GB RAM with 4 virtual systems to be run. I want each of them to start with 1GB RAM with maximum 2GB possible. This is not achievable since qemu pre-allocates the maximum balloon amount which is 2GBx4 systems . So to start all 4 systems the system needs 8GB RAM rather than 4GB RAM to start with although I have told initial balloon amount to be 1GB. To manage notifications about this bug go to: https://bugs.launchpad.net/qemu/+bug/1192065/+subscriptions