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RE: [Xen-devel] write page table in user mode

To: "Tim Deegan" <Tim.Deegan@xxxxxxxxxx>, "Keir Fraser" <Keir.Fraser@xxxxxxxxxxxx>
Subject: RE: [Xen-devel] write page table in user mode
From: "Tian, Kevin" <kevin.tian@xxxxxxxxx>
Date: Mon, 4 Feb 2008 22:24:01 +0800
Cc: "Su, Disheng" <disheng.su@xxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx
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Thread-topic: [Xen-devel] write page table in user mode
>From: Tim Deegan [mailto:Tim.Deegan@xxxxxxxxxx] 
>Sent: 2008年2月4日 19:01
>Nor do I (since as Kevin points out we don't count this separately) but
>with the increasing completeness of the emulator, we've already lost a
>lot of heuristics for unshadowing pages -- this is what the
>unshadow-after-three-writes heuristic is trying to fix, for 
>example.  It
>seems odd to be making the unshadowing more aggressive with 
>one hand and
>less aggressive with the other.

BTW, as a heads up we're trying another heuristic to take DMA page
into unshadow candidate, which requires Qemu's help indicating
whether data in ioreq is a DMA target. This should help capture one
vague area when released page tables are used by kernel drivers. 
DMA is normally one big factor for frequent page allocation/free. It's
also not affected by more complete emulator.

Now well, patch is just in progress and we need many experiments
to see how it behaves like compared to 3-write-unshadow, etc. But
We may be only able to get something after Chinese New Year
vacation. :-)


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