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[Xen-devel] Re: [PATCH v2.0 1/6] Add a config option for memory hot add

To: "Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx>
Subject: [Xen-devel] Re: [PATCH v2.0 1/6] Add a config option for memory hot add
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Wed, 08 Jul 2009 15:40:33 +0100
Cc: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
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On 08/07/2009 15:31, "Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx> wrote:

> Sorry that I didn't realize the purpose of the CONFIG_* options. But this
> optoin may be needed because:
> a) When memory hotplug, we need set the boot allocation bitmap memory to 512k
> when booting. So for small system, we can avoid that extra memory. Of course,
> maybe that can be removed after the allocation bitmap is removed al-together.
> b) When Memory hotplug, we can't adjust compatible guest's hv_virt_start
> anymore. I'm not sure how important it is, so I keep that for
> non-memory-hotplug support.

Can you explain the reasons for these limitations? I can't see why either
would be strictly necessary.

Also if you limit the bitmap memory to 512k during boot that wouldn't be
great since it limits us to 16GB doesn't it?

Another thought: you should kill x86_32 support if it simplifies your
patches. We really only need to support these big-iron features on x86_64 --
nearly everyone should be able to happily run x86_64 Xen by now.

 -- Keir

> Any idea?
> I will change the X86_MAX_PFN.

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