Re: [PATCH] virtio-balloon: do not attempt to release more than available pages

[Anthony Liguori <anthony@codemonkey.ws>]

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Rusty Russell wrote:
> On Sunday 09 March 2008 06:06:38 Marcelo Tosatti wrote:
>   
>> But making the driver robust against it seems sensate. I agree that
>> zeroing num_pages is hackish. What do you suggest?
>>     
>
> OK, after more discussion on IRC, this seems like the correct thing to do.
>
> 1) Allow more than 2G of pages.  It doesn't cost us much to break the 8TB
>    barrier.  This is an ABI change, so best to do this now.
>   

I don't think there's a compelling need to break the ABI.  If we truly 
ever needed to break the 8TB barrier, we could simply introduce another 
ballooning device.  virtio_pci relies on PFNs fitting into a 32-bit 
value so breaking the 8TB barrier here doesn't given it to us for free 
anyway.

Plus, we've released an external drivers package.  Breaking the ABI at 
this stage is going to cause user confusion.  Sure, the ABI isn't stable 
until 2.6.25 ships but I do think we should have a more compelling 
reason to do it if we truly have to.

> 2) Handle the case where we get nonsense from the host, which causes us to
>    wrap around.
>   

Here's my neither compiled nor tested version which should fix this 
problem without breaking the ABI.

Regards,

Anthony Liguori

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