Re: [Xen-devel][PATCH] don't split the whole large page while live migration with EPT

[Tim Deegan <Tim.Deegan@xxxxxxxxxx>]

At 13:47 +0100 on 16 Apr (1239889668), Xin, Xiaohui wrote:
> We haven't measure the performance yet.

But you're planning to? :)

> 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 splitted.

Log-dirty map reads happen with the target domain paused; all other
readers are easily made safe: build the new L1 table first and then
atomically change the l2 entry to point to it.

Cheers,

Tim.

> Thanks
> Xiaohui
> 
> -----Original Message-----
> From: Tim Deegan [mailto:Tim.Deegan@xxxxxxxxxx] 
> Sent: 2009??4??16?? 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?
> 
> Cheers,
> 
> Tim
> 
> -- 
> Tim Deegan <Tim.Deegan@xxxxxxxxxx>
> Principal Software Engineer, Citrix Systems (R&D) Ltd.
> [Company #02300071, SL9 0DZ, UK.]

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

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