Re: CPU hot-plug and RAM hot-add in virtual machines
- In reply to: Miroslav Lachman : "Re: CPU hot-plug and RAM hot-add in virtual machines"
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Date: Wed, 21 Jul 2021 20:56:58 UTC
On 21/07/2021 13:07, Miroslav Lachman wrote: > On 21/07/2021 12:45, Andriy Gapon wrote: >> On 21/07/2021 11:53, Miroslav Lachman wrote: >>> On 09/07/2021 13:16, Andriy Gapon wrote: > > [..] > >>> Thank you for your reply. I know nothing about system internals. Is >>> it too much work to implement it or just nobody from developers need >>> it thus nobody write the code? Virtualization is more and more >>> popular these days so I think it will be useful for many users. >> >> In my opinion, both would be big changes. >> At the moment we do not have any support for offlining / onlining CPUs >> and that would involve a lot of careful changes like safely updating >> CPU sets, various CPU masks, etc. >> >> Ditto for the memory. Updating page arrays, free memory accounting >> structures, possibly some memory maps, etc. >> >> Definitely not a weekend project. > > Thank you again. It really seems too complicated. Have you tried messing around with virtio_balloon(4)? It's the other way around though. You'd overprovision the VM, then balloon memory away and later on give it back, if needed.