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Re: [Xen-devel] I cannot get any message from domU by console / pv_ops d

To: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Subject: Re: [Xen-devel] I cannot get any message from domU by console / pv_ops domU kernel crashes with xen_create_contiguous_region failed
From: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
Date: Tue, 22 Dec 2009 14:58:47 +0000
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On Tue, 2009-12-22 at 14:32 +0000, Konrad Rzeszutek Wilk wrote:
> > >    (early) [    0.000000] Kernel panic - not syncing:
> > >    <3>xen_create_contiguous_region failed
> This implies you did not have enough DMA32 memory in the hypervisor for the 
> guest.
> Meaning at least 64MB.

Does this mean that every domU is allocating 64M for swiotlb by default?
That seems like an awful lot of wastage when the vast majority of guests
have no I/O device and therefore no need for swiotlb, especially given
that this is memory from a limited pool (OK, so 64G isn't that low a

If we are unable to automatically determine early enough whether a guest
needs swiotlb or not (which I suspect is the case without additional
tools support) then I think the old-style behaviour of only enabling
swiotlb in domU on explicit request matches the common case better.


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