Messages in this thread | | | Date | Tue, 5 Oct 2021 15:26:23 +0200 | Subject | Re: [PATCH v5 00/14] KVM: s390: pv: implement lazy destroy for reboot | From | Janosch Frank <> |
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On 9/20/21 15:24, Claudio Imbrenda wrote: > Previously, when a protected VM was rebooted or when it was shut down, > its memory was made unprotected, and then the protected VM itself was > destroyed. Looping over the whole address space can take some time, > considering the overhead of the various Ultravisor Calls (UVCs). This > means that a reboot or a shutdown would take a potentially long amount > of time, depending on the amount of used memory. > > This patchseries implements a deferred destroy mechanism for protected > guests. When a protected guest is destroyed, its memory is cleared in > background, allowing the guest to restart or terminate significantly > faster than before. > > There are 2 possibilities when a protected VM is torn down: > * it still has an address space associated (reboot case) > * it does not have an address space anymore (shutdown case) > > For the reboot case, the reference count of the mm is increased, and > then a background thread is started to clean up. Once the thread went > through the whole address space, the protected VM is actually > destroyed. > > This means that the same address space can have memory belonging to > more than one protected guest, although only one will be running, the > others will in fact not even have any CPUs. > > The shutdown case is more controversial, and it will be dealt with in a > future patchseries. > > When a guest is destroyed, its memory still counts towards its memory > control group until it's actually freed (I tested this experimentally)
@Christian: I'd like to have #1-3 in early so we can focus on the more complicated stuff.
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