Re: [Qemu-devel] [RFC] qmp interface for save vmstate to image

[Wenchao Xia <xiawenc@linux.vnet.ibm.com>]

于 2013-3-18 18:08, Paolo Bonzini 写道:
> Il 18/03/2013 10:04, Kevin Wolf ha scritto:
>> Oh, seems I misread this then. I thought this was about internal live
>> snapshots, which is a feature that I consider really useful. I'm not so
>> sure if saving the VM state as the disk contents of a qcow2 image is
>> really helpful.
>>
>> If zero clusters help a lot, then there's clearly something to improve
>> in the migration protocol, because it shouldn't send so many zeros in
>> the first place.
>
> Zero pages are sent as a single 9-byte entry (64 bits for the address
> and flags, 8 for the zero).
>
> I don't expect the migration stream to have a single zero cluster, since
> every page is prefixed by the 64 bits for the address and flags.
> Furthermore, the RAM data would be horribly unaligned because of this.
> 15-20% sectors or so would be read twice, since reading each page (4104
> bytes including the address and flags) would span 10 sectors (5120 bytes).
>
> Paolo
>
   I think in streaming case, zero page will be handled well. I use
qcow2 mainly for fseek() case, which may have some zero holes inside.

-- 
Best Regards

Wenchao Xia