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RE: [Xen-devel][PATCH] don't split the whole large page while live migra

To: Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Subject: RE: [Xen-devel][PATCH] don't split the whole large page while live migration with EPT
From: "Xin, Xiaohui" <xiaohui.xin@xxxxxxxxx>
Date: Thu, 16 Apr 2009 20:47:48 +0800
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Thread-index: Acm+j+790tKeLT8kQzCwWzjwIju3gAAAFTQw
Thread-topic: [Xen-devel][PATCH] don't split the whole large page while live migration with EPT
We haven't measure the performance yet. But since we did not lock the p2m table 
for p2m table reading, splitting the large page during live migration may be 
dangerous while other CPU wants to read the ept entries which are being 


-----Original Message-----
From: Tim Deegan [mailto:Tim.Deegan@xxxxxxxxxx] 
Sent: 2009年4月16日 20:36
To: Xin, Xiaohui
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-devel][PATCH] don't split the whole large page while live 
migration with EPT

At 13:33 +0100 on 16 Apr (1239888814), Xin, Xiaohui wrote:
> Before, when HVM guest live migration with EPT, we just write protect all the 
> EPT leaf entries.
> Then we know the dirty pages through ept_handle_violation(), and call 
> p2m_change_type()
> to put back the write access of the EPT entries. At that time when we use 
> large pages,
> we used to split the large page to 4K.
> It?s not necessary. Alternatively, we can just retain the large page entries,
> and put back the write access and mark dirty all the small pages in the large 
> page.
> The patch attached removes the splitting.

What effect does this have on live migration time/traffic under load?



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