Re: [Xen-devel] balloon question

["Zhang, Chunyu" <zhangcy@xxxxxxxxxxxxxx>]

hi george
>Please don't cross-post unless you need to.  These are coding
>questions, so xen-devel is the right place to ask this.
>
>On Thu, Apr 28, 2016 at 7:58 AM, Zhang, Chunyu <zhangcy@xxxxxxxxxxxxxx> wrote:
>>
>> hi all
>>
>> i have two question about ballon.
>>
>> 1.
>> cfg:
>>      memory=4096
>>      maxmem=4096
>>
>> no pod was set , no balloon is set .
>> when xl create, i find function decrease_reservation is call.
>> i did not why ?
>
>decrease_reservation is never initiated by the hypervisor -- it's
>normally initiated by the guest balloon driver; although I think it
>may also be initiated by other components, like hvmloader or qemu (not
>sure about that).  You'd have to figure out which component was making
>that hypercall, and then look in the logic to find out why it was
>doing so.
got it.
i will check  it.
>
>>
>> 2.  pod + balloon
>> cfg:
>>      memory=512
>>      maxmem=4096
>>
>>  decrease_reservation
>>     - p2m_pod_decrease_reservation
>>         - p2m_set_entry(p2m_invalid)
>>     - guest_remove_page
>>          - p2m_set_entry(p2m_invalid)
>>
>> in p2m_pod_decrease_reservation ,  gfn entry is set p2c_invalid.
>> but in guest_remove_page gfn entry is set p2c_invalid again.
>> i did not know  why?
>
>Did you not notice the "continue" between
>p2m_pod_decrease_reservation() and guest_remove_page()? :-)
oh....
i know the point(⊙﹏⊙)b
>
>p2m_pod_decrease_reservation() either does everything necessary (both
>reclaim the page and set the p2m entry) or nothing.  It will return 0
>to mean, "I didn't do anything, you still need to free the page", and
>1 to mean "I did everything, no need for you to do anything more."
got it, thank u very much.
>
> -George
>
>

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