Re: large page size virtio issues

[Anthony Liguori <aliguori-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>]

Hollis Blanchard wrote:
> On Wed, 2008-11-05 at 11:25 -0600, Anthony Liguori wrote:
>   
>> I think we should just have a VIRTIO_PFN_SHIFT define that is 
>> architecture specific.
>>
>> On x86, it'll be 4k.  You can make it whatever you want for PPC.
>> Fixing all architectures to be 4k is going to suck for architectures
>> with < 4k pages.
>>     
>
> So we're now in agreement that it should be hardcoded. I don't see much
> value in making the actual value arch-specific, but either way it will
> solve (at least part of, and maybe all of) my problem. Rusty?
>   

When you balloon pages, you need to pass something that points to the 
beginning of a page boundary.  If your page size is 2k, then if you are 
only able to pass 4k addresses, you can't below any page that happens to 
not be 4k aligned.

If you were going to make it common across all architectures, you would 
have to make it the smallest possible page size and that would break x86 
backwards compatibility.

Regards,

Anthony Liguori


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