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Re: [Xen-devel] Re: [PATCH] Support swap a page from user space tools --

To: "Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx>, Tim Deegan <Tim.Deegan@xxxxxxxxxxxxx>
Subject: Re: [Xen-devel] Re: [PATCH] Support swap a page from user space tools -- Was RE: [RFC][PATCH] Basic support for page offline
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Fri, 20 Mar 2009 09:28:52 +0000
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Thread-topic: [Xen-devel] Re: [PATCH] Support swap a page from user space tools -- Was RE: [RFC][PATCH] Basic support for page offline
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On 20/03/2009 09:16, "Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx> wrote:

>> Thanks for the description. I guess I will wait for your next
>> patch, which
>> should I think at least separate the foreign pagetable update hypercall from
> I think I have split that patch last night. There is no foreign page table
> hypercall anymore, instead, I just tried to enhance the current mmu_op. And
> this new "weird" swap is now named mmu_ext_exchange_page.(Is it really so
> weird to just pass the new mfn down?)

Ah yes, I found the email now. Well I'm still confused as to why it is
needed. It seems to me you could scan for all PTEs mapping old_pfn, stash
them in a list and temporarily make them not-present, and take a copy of
old_pfn. Then do a normal XENMEM_exchange: on failure revert all PTEs, on
success switch over all PTEs and copy old_pfn data into new_pfn. Well it is
more hypercalls (two updates per PTE) I suppose, but I doubt this matters
unless you're offlining a lot of pages, and we don't support offlining
memory banks really at the moment. Also some of this will potentially batch
up into multicalls or MMUOP_ lists nicely anyway.

 -- Keir

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