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Re: [Xen-devel] [PATCH] fix memory exchange hypercall.

To: Keir Fraser <keir@xxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] fix memory exchange hypercall.
From: Isaku Yamahata <yamahata@xxxxxxxxxxxxx>
Date: Thu, 15 Mar 2007 22:38:19 +0900
Cc: Tim Deegan <Tim.Deegan@xxxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, xen-ia64-devel@xxxxxxxxxxxxxxxxxxx
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On Thu, Mar 15, 2007 at 12:23:20PM +0000, Keir Fraser wrote:
> Whichever, I think we should sort it out one way or the other and change
> ia64 and/or x86 now. Or it'll never happen!

I see. To be honest I expected this kind of response.
I'll give it a try again, but it may take a while.

Could you explain about PGC_allocated and balloon?
What's the rationale when to clear/set PGC_allocate bit?

My understanding is as follows.
- PGC_allocated means +1 page reference count.
- It is neccessary for x86 paravirtualized domain to keep
  page from freeing.
- It doesn't make sense for x86 hvm domain so that it is only cleared
  by relinquish_memory().
- If the p2m entry is cleared which isn't followed by
  clearing PGC_allocaed and put_page() without any recording,
  there is no easy way to free the page until domain destruction.


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