Re: RFC: QEMU bumping memory limit and domain restore

[Yang Hongyang <yanghy@cn.fujitsu.com>]

On 06/02/2015 11:49 PM, Ian Campbell wrote:
> On Tue, 2015-06-02 at 15:08 +0100, Wei Liu wrote:
> [...]
>>> So here is a proof of concept patch to record and honour that value
>>> during migration.  A new field is added in IDL. Note that we don't
>>> provide xl level config option for it and mandate it to be default value
>>> during domain creation. This is to prevent libxl user from using it to
>>> avoid unforeseen repercussions.
>> [...]
>>> This field is mandated to be default value during guest creation to
>>> avoid unforeseen repercussions. It's only honour when restoring a guest.
>
> IMHO this means that the libxl API/IDL is the wrong place for this
> value. Only user and/or application serviceable parts belong in the API.
>
> So while I agree that this value need to be communicated across a
> migration, the JSON blob is not the right mechanism for doing so. IOW if
> you go down this general path I think you need a new
> field/record/whatever in the migration protocol at some layer or other
> (if not libxc then at the libxl layer).
>
> To my mind this "actual state" vs "user configured state" is more akin
> to the sorts of things which is in the hypervisor save blob or something
> like that (nb: This is not a suggestion that it should go there).
>
> IIRC Don also outlined another case, which is
>      xl create -p
>      xl migrate
>      xl unpause

Actually this is what COLO do. On primary, we must start using -p then
migrate to ensure the disk is consistent.

>
> Which might need more thought if any bumping can happen after the
> migrate i.e. on unpause?
>
>
> .
>

-- 
Thanks,
Yang.