Re: [Xen-devel] Question about mapping hvm‘s memory to dom0

[George Dunlap <George.Dunlap@xxxxxxxxxxxxx>]

On Tue, Jul 2, 2013 at 3:26 PM, Kai Luo <kluo@xxxxxxxxxx> wrote:
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>
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> ----- Original Message -----
>> From: "George Dunlap" <dunlapg@xxxxxxxxx>
>> To: "Kai Luo" <kluo@xxxxxxxxxx>
>> Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, "Dietmar Hahn" 
>> <dietmar.hahn@xxxxxxxxxxxxxx>
>> Sent: Tuesday, July 2, 2013 9:43:27 PM
>> Subject: Re: [Xen-devel] Question about mapping hvmâs memory to dom0
>>
>> On Tue, Jul 2, 2013 at 2:31 PM, Kai Luo <kluo@xxxxxxxxxx> wrote:
>> >
>> > I know every frame has a struct to help xen manage memory,in addition to
>> > normal mapping,when the frame refcount increases for hvm domain?page
>> > sharing?Or something else?
>>
>> (Please don't top-post.)
>>
>> I'm sorry, do you mean, "When does the frame refcount increase?"
>>
>> I'm afraid it's a bit complicated and not written down anywhere.  In
>> *general* the refcount increases whenever the page is mapped by a
>> domain, including dom0; as long as it has dom0 has domU pages mapped,
>> their reference counts will be at least 1 and the domain cannot be
>> destroyed.
>
>    Sorry about that top-post.I can think out circumstance that refcount 
> increases which shows as below:(1)when the frame is assigned to a 
> domain;(2)when the frame is mapped to dom0 by the given xc* interface.
>    Without people's intervention,are there any other condition that refcount 
> increasesïFor exampleïthe content in pages of different domains are sameïso 
> they share only one frame and the refcount increases?

Page sharing is a fairly new feature, and I'm not exactly sure how
refcounting works in that case.  Tim / Andres, care to comment?

 -George

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