Re: [PATCH RFC] hotplug-memory: refactor online_pages to separate zone growth from page onlining

[Jeremy Fitzhardinge <jeremy@goop.org>]

Dave Hansen wrote:
> On Wed, 2008-04-02 at 14:35 -0700, Jeremy Fitzhardinge wrote:
>   
>> Dave Hansen wrote:
>>     
>>> Oh, once we've let Linux establish ptes to it, we've required that the
>>> hypervisor have it around?  How does that work with the balloon driver?
>>> Do we destroy the ptes when giving balloon memory back to the
>>> hypervisor?
>>>       
>> Yep.  It removes any mapping before handing it back to the hypervisor.
>>     
>
> Wow.  So does Xen ever use PSE to map kernel data?  That sucks.
>   

Not at present.  But I'd like to change it to manage memory in largepage 
chunks so that we can.

> Yeah, but I'm just talking about hotplugged memory.  When we add it, we
> don't have to map the added pages (since they're highmem) and don't have
> to touch their contents and zero them out, either.  Then, the balloon
> driver can notice that the memory is too large, and start to balloon it
> down.
>   

I didn't think x86-64 had a notion of highmem.

How do you prevent the pages from being used before they're ballooned out?

>> Everything also applies to x86-64.
>>     
>
> Not really, though.  We don't have the page->flags shortage or lack of
> vmemmap on x86_64.

Right now, I'd rather have a single mechanism that works for both.

    J