Re: [Qemu-devel] Re: [PATCH 2 of 5] add can_dma/post_dma for direct IO

[Avi Kivity <avi@redhat.com>]

Thiemo Seufer wrote:

  

>> I agree that we shouldn't expect memory to be contiguous, in order to  
>> properly support hotplug.  But I see zero value in trying to support  
>> large memory configurations on 32-bit in 2008.  This is what 64-bit  
>> systems are for!  If Xen has a problem with 64-bit hosts, we can try to  
>> accommodate it, but to have 32-bit qemu/tcg
>>     
>
> Running x86-64 binaries on a (non-x86) 32-bit host is IMHO quite an
> obvious application for qemu/tcg.
>   

I agree.  I don't think running guests with >2GB of RAM on 32-bit hosts 
is a good idea, though.  Instruction set, physical address space width, 
and actual maximum memory size supported are very different things.

I'm sure you don't want qemu to swap memory in and out of its address 
space (which is what Xen does).

>> or qemu/kvm support large address spaces is pointless IMO.
>>     
>
> Interestingly, Virtualbox just started to support
> 64-bit-target-on-32-bit-host.
>   

That makes sense on Windows, where 32-bit hosts still have an advantage 
over 64-bit.  But again, that's very different from supporting a large 
address space.

Want 64-bit guests? sure, qemu/tcg can handle it, as well as qemu/kvm 
(on a 64-bit host).  Want lots of memory for your CAD 
application/openoffice docs/qemu guests?  Use a 64-bit host.

-- 
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