Date: Wed, 21 Jul 2021 21:56:58 +0100 From: Johannes Totz <johannes@jo-t.de> To: freebsd-stable@freebsd.org Subject: Re: CPU hot-plug and RAM hot-add in virtual machines Message-ID: <sda1mr$10se$1@ciao.gmane.io> In-Reply-To: <c647b6b8-f924-e697-bacd-a29f31ed9cae@quip.cz> References: <4336a1bf-d826-dba3-9ec1-9b48cf7cd177@quip.cz> <70033628-bc3a-24d2-4c65-9a3b9c1c66d5@FreeBSD.org> <b849f8d3-661e-f5c5-c5e6-594219dbd842@quip.cz> <14d647fe-5bc3-b69e-e074-6202b2418d22@FreeBSD.org> <c647b6b8-f924-e697-bacd-a29f31ed9cae@quip.cz>
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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.
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