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To:     Paolo Bonzini <pbonzini@redhat.com>,
        "Maciej S. Szmigiero" <mail@maciej.szmigiero.name>,
        Sean Christopherson <seanjc@google.com>
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From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat GmbH
Subject: Re: [PATCH 2/2] KVM: Scalable memslots implementation
Message-ID: <b9aacf06-de2b-b831-6210-25191dd1b0ac@redhat.com>
Date:   Wed, 3 Feb 2021 14:52:42 +0100
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On 03.02.21 14:46, Paolo Bonzini wrote:
> On 03/02/21 14:44, David Hildenbrand wrote:
>> BTW: what are your thoughts regarding converting the rmap array on
>> x86-64 into some dynamic datastructre (xarray etc)? Has that already
>> been discussed?
> 
> Hasn't been discussed---as always, showing the code would be the best
> way to start a discussion. :)

If only a workday would have more hours :)

> 
> However, note that the TDP MMU does not need an rmap at all.  Since that
> one is getting ready to become the default, the benefits of working on
> the rmap would be quite small and only affect nested virtualization.

Right, but we currently always have to allocate it.

8 bytes per 4k page, 8 bytes per 2M page, 8 bytes per 1G page.

The 4k part alone is 0.2% of the memblock size.

For a 1 TB memslot we might "waste" > 2 GB on rmap arrays.

(that's why I am asking :) )

-- 
Thanks,

David / dhildenb