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RE: [Xen-devel] Re: [PATCH] Support swap a page from user spacetools --

To: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxxxx>
Subject: RE: [Xen-devel] Re: [PATCH] Support swap a page from user spacetools -- Was RE: [RFC][PATCH] Basic support for page offline
From: "Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx>
Date: Fri, 20 Mar 2009 18:13:13 +0800
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Cc: Tim Deegan <Tim.Deegan@xxxxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
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Thread-topic: [Xen-devel] Re: [PATCH] Support swap a page from user spacetools -- Was RE: [RFC][PATCH] Basic support for page offline
Keir Fraser <mailto:keir.fraser@xxxxxxxxxxxxx> wrote:
> On 20/03/2009 10:03, "Keir Fraser" <keir.fraser@xxxxxxxxxxxxx> wrote:
>>>> Ah, you do a suspend-cancel/fast-resume?
>>> Yes, that's suggested by Tim and I think that's meet our purpose quite
>>> well. 
>> Okay, then I suggest you extend XENMEM_exchange so that in.mem_flags can
>> tell that hypercall to copy data from old to new pages. XENMEMF_copy_data?
> Even this may not work. Old grants will reference the old
> page. Subsequent
> attempts by a backend to map the grant will fail. And the
> resulting failed
> I/Os will probably make the frontend driver throw a fit. Getting this
> working with suspend-cancel seems pretty tricky.

If there is grant map for it, I think we will fail since the reference is not 1 
when XENMEM_exchange.

Or do you mean there is a reference in grant table but is not mapped still? 
Will the refrence count be added when a page is granted? I'm not quite sure 
about this, but I think that will be same to original XENMEM_exchange. If yes, 
we may have to update the grant information?

The normal save-restore method may cause service broken, I think that's the 
reason of choosing the suspend-cacel method.

Yunhong Jiang

> -- Keir
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