linux-kernel - Re: [PATCH RFC 04/15] KVM: Implement ring-based dirty memory tracking

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Message-ID: <8843d1c8-1c87-e789-9930-77e052bf72f9@redhat.com>
Date:   Tue, 10 Dec 2019 14:31:54 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Jason Wang <jasowang@...hat.com>, Peter Xu <peterx@...hat.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>
Subject: Re: [PATCH RFC 04/15] KVM: Implement ring-based dirty memory tracking

On 10/12/19 14:25, Michael S. Tsirkin wrote:
>> There is no new infrastructure to track the dirty pages---it's just a
>> different way to pass them to userspace.
> Did you guys consider using one of the virtio ring formats?
> Maybe reusing vhost code?

There are no used/available entries here, it's unidirectional
(kernel->user).

> If you did and it's not a good fit, this is something good to mention
> in the commit log.
> 
> I also wonder about performance numbers - any data here?

Yes some numbers would be useful.  Note however that the improvement is
asymptotical, O(#dirtied pages) vs O(#total pages) so it may differ
depending on the workload.

Paolo