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Subject: Re: [PATCH RFC 00/15] KVM: Dirty ring interface
To:     Peter Xu <peterx@redhat.com>, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org
Cc:     Sean Christopherson <sean.j.christopherson@intel.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        "Dr . David Alan Gilbert" <dgilbert@redhat.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        "Michael S. Tsirkin" <mst@redhat.com>
References: <20191129213505.18472-1-peterx@redhat.com>
From:   Jason Wang <jasowang@redhat.com>
Message-ID: <776732ca-06c8-c529-0899-9d2ffacf7789@redhat.com>
Date:   Wed, 4 Dec 2019 18:39:48 +0800
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On 2019/11/30 =E4=B8=8A=E5=8D=885:34, Peter Xu wrote:
> Branch is here:https://github.com/xzpeter/linux/tree/kvm-dirty-ring
>
> Overview
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
>
> This is a continued work from Lei Cao<lei.cao@stratus.com>  and Paolo
> on the KVM dirty ring interface.  To make it simple, I'll still start
> with version 1 as RFC.
>
> The new dirty ring interface is another way to collect dirty pages for
> the virtual machine, but it is different from the existing dirty
> logging interface in a few ways, majorly:
>
>    - Data format: The dirty data was in a ring format rather than a
>      bitmap format, so the size of data to sync for dirty logging does
>      not depend on the size of guest memory any more, but speed of
>      dirtying.  Also, the dirty ring is per-vcpu (currently plus
>      another per-vm ring, so total ring number is N+1), while the dirty
>      bitmap is per-vm.
>
>    - Data copy: The sync of dirty pages does not need data copy any more,
>      but instead the ring is shared between the userspace and kernel by
>      page sharings (mmap() on either the vm fd or vcpu fd)
>
>    - Interface: Instead of using the old KVM_GET_DIRTY_LOG,
>      KVM_CLEAR_DIRTY_LOG interfaces, the new ring uses a new interface
>      called KVM_RESET_DIRTY_RINGS when we want to reset the collected
>      dirty pages to protected mode again (works like
>      KVM_CLEAR_DIRTY_LOG, but ring based)
>
> And more.


Looks really interesting, I wonder if we can make this as a library then=20
we can reuse it for vhost.

Thanks