[Xen-devel] RE: [RFC][PATCH] Basic support for page offline

["Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx>]

>-----Original Message-----
>From: Tim Deegan [mailto:Tim.Deegan@xxxxxxxxxx] 
>Sent: 2009年2月16日 22:31
>To: Jiang, Yunhong
>Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
>Subject: Re: [RFC][PATCH] Basic support for page offline
>
>At 04:48 -0500 on 15 Feb (1234673293), Jiang, Yunhong wrote:
>> > The reference counting in update_pgtable_entry() is confusing -- it
>> > should probably always do reference counting for both the 
>old and new
>> > entries; that seems more robust than only doing the decrements
>> > there and
>> > manually setting count_info and type_info on the new page 
>in replace_page.
>> 
>> Sure, I will do like this.
>
>In fact, it should use the existing PTE-updating code -- I 
>suspect that,
>for example, your code won't work at all on a guest that has shadow
>pagetables enabled.

Yes, we need work differently depends on guest's paging mode. I forgot PV guest 
will use shadow mode for log dirty.
Just as you said, doing this in user space tools will be much simpler, I will 
consider more on that option.


>
>> > The tools patch is enormous, and seems to copy big chunks of
>> > xc_domain_save into a new file.  And since Xen is now 
>doing the hard
>> > work of pagetable manipulation, I don't think you even 
>need to suspend
>> > the guest -- just pausing it should be enough and is much easier.
>> 
>> But I'm not sure if we can update the P2M table from Xen side, that's
>> the reason I did the it in the user space.
>
>In that case, why don't you update the pagetables from the tools as
>well?  That way you'd avoid walking the guest pagetables in Xen.  You
>could make all the PTE changes, try to free the page, and if it still
>doesn't work (because there's some other refcount held), put 
>things back
>the way they were.


>
>Tim.
>
>-- 
>Tim Deegan <Tim.Deegan@xxxxxxxxxx>
>Principal Software Engineer, Citrix Systems (R&D) Ltd.
>[Company #02300071, SL9 0DZ, UK.]
>

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