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Subject: Re: [PATCH 2/2] KVM: Scalable memslots implementation
To:     Paolo Bonzini <pbonzini@redhat.com>,
        "Maciej S. Szmigiero" <mail@maciej.szmigiero.name>,
        Sean Christopherson <seanjc@google.com>
Cc:     Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Igor Mammedov <imammedo@redhat.com>,
        Marc Zyngier <maz@kernel.org>,
        James Morse <james.morse@arm.com>,
        Julien Thierry <julien.thierry.kdev@gmail.com>,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
        Huacai Chen <chenhuacai@kernel.org>,
        Aleksandar Markovic <aleksandar.qemu.devel@gmail.com>,
        Paul Mackerras <paulus@ozlabs.org>,
        Christian Borntraeger <borntraeger@de.ibm.com>,
        Janosch Frank <frankja@linux.ibm.com>,
        Cornelia Huck <cohuck@redhat.com>,
        Claudio Imbrenda <imbrenda@linux.ibm.com>,
        Joerg Roedel <joro@8bytes.org>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org
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From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat GmbH
Message-ID: <5efd931f-9d69-2936-89e8-278fe106616d@redhat.com>
Date:   Wed, 3 Feb 2021 14:44:20 +0100
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>> The new implementation also uses standard kernel {rb,interval}-tree
>> and hash table implementation as its basic data structures, so it
>> automatically benefits from any generic improvements to these.
>>
>> All for the low price of just 174 net lines of code added.
> 
> I think the best thing to do here is to provide a patch series that
> splits the individual changes so that they can be reviewed and their
> separate merits evaluated.
> 
> Another thing that I dislike about KVM_SET_USER_MEMORY_REGION is that
> IMO userspace should provide all memslots at once, for an atomic switch
> of the whole memory array.  (Or at least I would like to see the code;
> it might be a bit tricky because you'll need code to compute the
> difference between the old and new arrays and invoke
> kvm_arch_prepare/commit_memory_region).  I'm not sure how that would
> interact with the active/inactive pair that you introduce here.
> 

+1

One issue I am aware of is resizing/splitting slots, especially due to 
arrays like rmap + dirty bitmaps.

BTW: what are your thoughts regarding converting the rmap array on 
x86-64 into some dynamic datastructre (xarray etc)? Has that already 
been discussed?

> Paolo
> 


-- 
Thanks,

David / dhildenb