KVM Forum 2018

Memory hot(un)plug is a complicated matter. Especially when it comes to reliable memory hotunplug. While some architectures in KVM support memory hot(un)plug (e.g. x86), others have limited or no support (e.g. s390x).

Most hardware interfaces (like ACPI) are clearly focused on the concept of DIMMs. This usually implies that only fairly huge pieces of memory can be plugged and unplugged, whereby the latter can be problematic and easily fail.

In some virtual environments, people use ACPI for memory hotplug and balloon devices (e.g. virtio-balloon) as a mean for more reliable unplug of memory - which has a different set of restrictions.

In this talk, an introduction to the topic is given, the involved problems are outlined and virtio-mem is introduced, providing a single paravirtualized interface for fine grained memory hot(un)plug.