Re: [PATCH] kvm tools: Use mmap for working with disk image V2

[Avi Kivity <avi@redhat.com>]

On 04/10/2011 11:23 AM, Gleb Natapov wrote:
> >
> >  A creative idea, but I don't think it will work.  On EPT hosts we
> >  don't have accessed/dirty bits so you have to incur at least write
> >  faults to track dirty data and perhaps read faults to gather recency
> >  information.  On non-EPT you have to scan page tables to find out
> >  what you have to write out, and flush TLBs.  Cache misses, which
> >  you'd expect there to be quite a few, would stall the vcpu (unless
> >  you use asynchronous page faults) and contribute less information to
> >  the host than virtio-blk (location of access but not size).  Write
> >  misses are converted to read-modify-write operations.
> >
> Guest kernel can keep track of all modified sectors and pass it to
> hypervisor with sync command.

Should probably do the same for reads, to take advantage of batching.

This can be easily implemented using the qemu ivshmem device, if someone 
wants to try it out.

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