Re: [RFC 09/37] KVM: s390: protvirt: Implement on-demand pinning

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On 01.11.19 09:50, Claudio Imbrenda wrote:
On Thu, 31 Oct 2019 18:30:30 +0100
David Hildenbrand <david@xxxxxxxxxx> wrote:

On 31.10.19 16:41, Christian Borntraeger wrote:


On 25.10.19 10:49, David Hildenbrand wrote:
On 24.10.19 13:40, Janosch Frank wrote:
From: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>

Pin the guest pages when they are first accessed, instead of all
at the same time when starting the guest.

Please explain why you do stuff. Why do we have to pin the hole
guest memory? Why can't we mlock() the hole memory to avoid
swapping in user space?

Basically we pin the guest for the same reason as AMD did it for
their SEV. It is hard

Pinning all guest memory is very ugly. What you want is "don't page",
what you get is unmovable pages all over the place. I was hoping that
you could get around this by having an automatic back-and-forth
conversion in place (due to the special new exceptions).

we're not pinning all of guest memory, btw, but only the pages that are
actually used.

Any longer-running guest will eventually touch all guest physical memory (e.g., page cache, page shuffling), so this is only an optimization for short running guests.

--

Thanks,

David / dhildenb





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